Mopdas
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Undead will definitely defeat elves on a map where it's possible to arrive in the second week.
Or, if the elf is in a castle (and I don't know where it will get wood to build a fortress, let alone a stronghold or castle), then the undead will take all the good stuff on the map and become invincible, outleveling them by 5-8 levels!
If the undead doesn't have a plague tent, and it's lucky enough to dodge archer attacks, then we will win.
But, any thinking player can take Chaos against the elf, come in, and blast the archers, and that's it. And the elves don't have anything else in the early stages.