Delirium — Thraben Foulbloods gets +1/+1 and has menace as long as there are four or more card types among cards in your graveyard. (A creature with menace can't be blocked except by two or more creatures.)
Menace only matters as blockers are chosen. Causing Thraben Foulbloods to gain menace after blockers are chosen won’t cause it to become unblocked.