1mana monsters

What on Earth happened to your spelling/grammar in that post? o_0
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Anyway, I'd get Skeleton changed as its ability is a sac ability. It effectively went from 2mana sac to 4mana sac. Now, we can't ask for the skull it drops to be weaker, so the only alternative is to reduce the sac of Skeleton itself.
I think it's more of a proper balance issue than a minor after-tweak.