Easter eggs in Heroes.

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Also, I suggest that the moderators rename this topic because it has already outlived its usefulness and is gradually transitioning into something else.

Well said. We should ask them to do that.

Added 40 minutes later
I delved deep into the game (in the texts.pak file) and found the abilities of the Crystal Dragon. Large creature, flying creature, acid breath, crystal skin.
Crystal Skin: The Crystal Dragon is immune to direct creature-killing abilities, such as: "Grasping Strike," "Cleaving Sword," "Accurate Shot," etc.