Long ago, the Undead had percentage debuffs built into the Library and Monument replacements. They efficiently weakened the Undead in the right way, but I ended up getting rid of those, because it was possible to get around them (got -50% science from your library? Sell your library right after buying a university!). But now, Yair has given us percentage stat changes that cannot be escaped, because they're built into all cities! So please welcome a new, more efficiently debuffed Undead!