Game source code made from these reverse engineering notes available in this repository.
First, the resources we have available to use to reverse engineer the game.
Game Guides:
- http://www.jellyneo.net/?go=invasion_of_meridell
- http://www.neopets.com/~happylark (mirror)
- http://www.neopets.com/~Demeanours (mirror)
- http://www.neopets.com/~GoldEyeGriffin (mirror)
- http://pcal11.tripod.com/million/id30.html
- http://www.thedailyneopets.com/neopets-games/invasion-of-meridell/
- https://www.neofriends.net/threads/guide-invasion-of-meridell-in-depth.26528/
- http://www.neocodex.us/forum/topic/109241-invasion-of-meridell-guide/
- http://neopointsdeals.com/neopets-invasion-of-meridell-guide/
- http://www.angelfire.com/pop2/krillin373/invasionm.html
- https://www.pinkpt.com/neodex/index.php?title=Invasion_of_Meridell
Youtube Videos:
- https://www.youtube.com/watch?v=QJCtRCyfVww (levels 1, 2, 3)
- https://www.youtube.com/watch?v=644qdG2yd1w
2005 Battle Strategy Clone of game (javascript, v2 of IOM rather than v3):
[2015] Java Clone of game (author = darkflagrance):
As I reviewed the guides still available, I noted something unexpected.
There appear to have been multiple iterations of IOM.
The first version was just what we now call 'wave 1', missing missions 6-10. It seemed to last for only a short time, as it's only mentioned briefly in a single guide.
The second version added 'wave 2', and it's state is best described in this guide - it's divergences from version 3 (the final version) are that it appears Grarrl/Buzz couldn't enchant and block skeith teleport and grundo heal, and as a result moehog/techo couldn't disenchant those enchantments, and thus it made more sense to ditch your weak units (as opposed to version 3, where you virtually always keep your original units). This second version seemed to exist for some time, as I found 2 guides explicitly following it, and a few others that could be pointing to it.
The third version appears to have added the enchantment concept, and made a slight tweak to item spawns. Additionally, I think but cannot verify that Grarrl/Buzz stats were changed - instead of being identical, Buzz was changed to strong defense / weak attack, and Grarrl was made strong attack / weak defense. This third version also existed for a while, as it has the most guides describing it.
This clone attempts to match the third version of the game.
Note, the Java Clone author also notes these differences, saying "There have been multiple versions of Invasion of Meridell over the years, with different mechanics and items sets."
The 2015 Java Clone is a complete clone of the game - albeit imperfect (his goal seemed to be to recreate the experience and adjust the values as he saw fit, not necessarily to perfectly match the original game).
Our reverse engineering strategy is to start with the values in the 2015 Java Clone, then attempt to correct them based off our other resources (guides/videos).
In terms of trust...
- [Highest Trust] Images of the game from guides/youtube videos, as they are screencaps of the actual game being played (and there was no value in faking them at the time)
- [Medium Trust] Text from guides / youtube video description, as they were written while the actual game was live. Note that some guides have lower trust as they describe v2 of the game (and we're cloning v3)
- [Low Trust] The 2015 Java clone falls in this category, as it was written 4 years after the game disappeared
With that in mind, we will cycle through each section of the game, review the Java values, and correct them.
All treasures were correct in the 2015 Java clone, verified by numerous screenshots online. No changes necessary.
- Mission 1 = Health_Potion, verified in screenshots
- Mission 2 = Potion_of_Fortitude, verified in screenshots
- Mission 3 = Mega_Potion, verified in screenshots
- Mission 4 = Potion_of_Well-Being, verified in screenshots
- Mission 5 = Potion_of_Fortitude, verified in screenshots
- Mission 6 = Potion_of_Well-Being, verified in screenshots. (Java clone incorrectly puts Mega_Potion here)
- Mission 7 = Potion_of_Fortitude, verified in screenshots. (Java clone incorrectly puts Potion_of_Well-Being here)
- Mission 8 = Mega_Potion, verified in screenshots. (Java clone incorrectly puts Potion_of_Fortitude here)
- Mission 9 = ??? (Java clone puts Mega_Potion here)
- Mission 10 = ??? (Java clone puts Potion_of_Well-Being here)
There are no records in guides/videos from what potions are in Missions 9 and 10.
We've already established that the Java clone was incorrect in its values for Missions 6, 7, and 8 - so it is likely incorrect for 9 and 10 as well.
Pattern-wise in the 8 missions we were able to verify, there isn't a lot to go on.
Missions 3-8 go Mega / Well-Being / Fortitude and then Well-Being / Fortitude / Mega, which could indicate a recurring pattern which would next become Fortitude / Mega / Well-Being (popping the left-most element and putting it on the right).
There are only 4 potions, but 10 missions - so two potions (at least) would need to be used 3 times. We already see Fortitude being used 3 times, Mega and Well Being both twice, and Health just once... but then again, the Health potion seems basic, and may just be intended to be on the introductory level.
As all potions heal pets to full health and thus have no affect on gameplay other than asthetics, I've decided to just let this go and just go with the below values:
- Mission 9 = Potion_of_Well-Being. (Java clone puts Mega_Potion here)
- Mission 10 = Health_Potion. (Java clone puts Potion_of_Well-Being here)
Every mission will spawn four items - two Attack items, and two Defense items.
There is some randomness in which weapon combinations will spawn. For example, in Mission 4 both the Magic_Force_Spell and the Bow are in the spawn pool - the possible spawns are two Bows, two Magic_Force_Spells, or one of each. Because of this, just because an item does not appear in a screenshot does not mean we can 100% rule it out.
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Mission 1 = ["Mace", "Broadsword"]. Verified in screenshots
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Mission 2 = ["Bow", "Hammer"]. Two screenshots have double bows. One screenshot shows a broadsword, which was likely picked up in Mission 1 and then dropped here when a new weapon was picked up. The Java clone includes Hammer, and this guide includes hammer (albeit for iom v2).
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Mission 3 = ["Magic_Force_Spell", "Magic_Force_Spell"]. We have three unique game screenshots, all three of which have double Magic_Force_Spell spawned. The Java clone includes Berserker_Battleaxe as a possible spawn here - but I believe that is incorrect. None of our three unique screenshots support that. Also this guide which shows the items his team holds after beating Mission 3 and Mission 4, and in neither of them does any soldier have a Berserker_Battleaxe, even though it would be far better than the Magic_Force_Spell they are holding. So with that, I'm removing Berserker_Battleaxe from this spawn, and doing double Magic_Force_Spell, which fits all our screenshots and the guide. Follow-up note, this guide which is of v2 of IOM shows "Ax" as one of the attack items in this level, it is likely it was included in v2 but removed in v3.
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Mission 4 = ["Magic_Force_Spell", "Bow"]. Both Magic_Force_Spell and Bow are verified in screenshots showing the start of a Mission 4 level, giving us a high degree of certainty. The only variable is that the text in the description/guide on this video suggests a Berserker_Battleaxe should spawn in this level. We're going to assume that textual guide was in error, and trust the screenshots.
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Mission 5 = ["Berserker_Battleaxe", "Berserker_Battleaxe"]. The Java clone includes Magic_Force_Spell as a possible spawn here. I believe that is incorrect - all three unique game screenshots we have include double Berserker_Battleaxe. In Mission 3 we concluded that the Java Clone removed one Magic_Force_Spell spawn and replaced it with a Berserker_Battleaxe spawn, so it's not far-fetched to believe it did the opposite here - and our screenshots support the theory.
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Mission 6 = ["Sword_of_Deflection", "Sword_of_Deflection"]. Our one start of match screenshot has double Sword_of_Deflection. On a mid-game screenshot, a Berserker_Battleaxe is seen. However, it is within the path of the Techo, who likely dropped it to pickup a Sword_of_Deflection - so I believe the Berserker_Battleaxe was not spawned in this Mission, but just carried over from the previous mission and then dropped.
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Mission 7 = ["Double_Sword", "Halberd"]. We have two Mission 7 screenshots, and both are double Halberds. This guide notes that it's unnecessary to pick up Halberds here, as their attack bonuses (+4) aren't any better than what you already have. The Java clone includes "Double_Sword" here, which is identical in stats to the Sword of Deflection from the last level but without the ability to disenchant. I elected to keep this spawn chance here, even though not supported by screenshots, because the java clone has it, and it fits in with the guide's note that the weapons here aren't worth picking up because they aren't better than what you already have (so gameplay is unchanged if I'm wrong and its Halberd). Also if Double_Sword does not go here... then it doesn't have a mission it spawns in. Follow-up note - this guide, which is of iom v2 (with no enchantments) puts the double sword in mission 6 instead of the Sword of Deflection. That tells us that either double sword was removed in v3, or it was put as an alternative spawn in mission 7 as we have it.
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Mission 8 = ["Magic_Lightening_Spell", "Magic_Lightening_Spell"]. Single screenshot we have shows double Magic_Lightening_Spell. Text on this video notes that you need to pickup a Magic_Lightening_Spell here for your Grundo. Java clone includes double "Magic_Lightening_Spell", so we'll roll with it.
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Mission 9 = ["Double_Axe", "Double_Axe"]. The java clone values are matched by this guide, though the guide is for v2 of IOM (and not v3) - so we'll go with these values.
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Mission 10 = ["Double_Axe", "Magic_Lightening_Spell"]. The java clone values are matched by this guide, though the guide is for v2 of IOM (and not v3) - so we'll go with these values.
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Mission 1 = ["Magic_Staff_of_Thunder", "Magic_Staff_of_Thunder"]. All screenshots and guides show double Magic_Staff_of_Thunder, as does the Java clone.
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Mission 2 = ["Amulet_of_Teleportation", "Amulet_of_Teleportation"]. All start of game screenshots show double Amulet_of_Teleportation. Some mid game screenshots show Magic_Staff_of_Thunder, which we assume was dropped to pick up an Amulet_of_Teleportation.
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Mission 3 = ["Helmet", "Shield"]. We have 3 unique screenshots, all of which show double Helmet. However this guide shows his team with Shields after beating Mission 3. Therefore, we accept the Java clone value of Helmet and Shield.
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Mission 4 = ["Plate_Armor", "Magic_Cloak_of_Invisibility"]. We have three unique screenshots of this Mission, all of which show double Plate_Armor here. The Java clone does not include Plate_Armor as a spawn option, including instead Amulet_of_Teleportation and Magic_Cloak_of_Invisibility. This guide shows his team with a Magic_Cloak_of_Invisibility after beating this mission. Therefore, we take the Java clone value, but swap Amulet_of_Teleportation for Plate_Armor.
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Mission 5 = ["Counter_Enchantment_Helmet", "Counter_Enchantment_Helmet"]. We have three screenshots here, all of which show only Counter_Enchantment_Helmet. The Java clone uses (normal) Helmet and Shield as spawn options. We know "Helmet" is wrong and should be "Counter_Enchantment_Helmet". The only evidence for "Shield" is that the Java clone includes it, but since we already know the Java clone is wrong, we'll just go double "Counter_Enchantment_Helmet" here (which matches all screenshots). This makes up for the next mission, where the Java clone spawns too many Counter_Enchantment_Helmet so we need to reduce them.
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Mission 6 = ["Plate_Armor", "Plate_Armor"]. All screenshots solely support Plate_Armor spawning here. The Java clone has a double Counter_Enchantment_Helmet here. We'll roll with double Plate_Armor to support the screenshots.
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Mission 7 = ["Chainmail", "Chainmail"]. We have only 2 screenshots, which both have double Chainmail. This guide notes that it's unnecessary to pick up Chainmails here, as their defense bonuses (+4) aren't any better than what you already have. The Java clone includes Leather_Armor here alongside Chainmail. Leather_Armor is supposed to be in Mission 8 according to screenshots, but the Java clone is missing it - so assume the Java clone is wrong here and misplaced Leather_Armor, but it's really supposed to be double Chainmail.
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Mission 8 = ["Leather_Armor", "Leather_Armor"]. Our sole screenshot has double Leather_Armor. The Java clone has Plate_Armor and Chainmail as the spawn options, so it's wrong for leaving out Leather_Armor. We cannot know whether double Leather_Armor or Leather_Armor + X is correct here. I elect to go with double Leather_Armor to match the screenshots. The core concept seems to be that this armor (at +3) is worse than what you already have, but better than nothing. Including Plate_Armor (+5) or Chainmail (+4) would go against that concept.
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Mission 9 = ["Amulet_of_Teleportation", "Chainmail"]. The java clone values are matched by this guide, though the guide is for v2 of IOM (and not v3) - so we'll go with these values.
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Mission 10 = ["Plate_Armor", "Chainmail"]. The java clone values are matched by this guide, though the guide is for v2 of IOM (and not v3) - so we'll go with these values.
All foes spawns were correct in the Java clone for Missions 1-8 that we were able to verify with screenshots. Therefore, we just trust the Java clone to be correct for Missions 9 and 10.
Reviewing all game board screenshots, we see there are all four sets of two mountains, and they are connected symmetrically by row. Each set of two mountains may spawn on the far right and left, or one block in from the right and left, or in the middle two squares. The only exception is the top-most row, which if it spawns in the middle, then the left mountain remains an empty space (because in later levels an enemy troop will spawn in that square).
The villages always spawn in rows 2-4 (counting from the bottom up). There are two villages per row, and each row has one in the first 5 squares and one in the second 5 squares.
Potions always spawn in the same two slots.
Attack/Defense items always spawn in rows 2-6 (counting from the bottom up). Note that they only spawn in empty spaces, calculated AFTER everything else has spawned. This means villages, mountains, and potions spawn before them.
I believe that it is a purely random chance, but my screenshots make it seem like rows 4-6 have a greater chance of getting items. I believe this is just due to the fact that villages spawn in the lower rows, reducing the number of empty squares and thus reducing the likelihood for items to spawn there.