Name: Bloodstained altar
FOR THE DARK GODS! (active) - Sacrifice one random Acolyte of greed to the great old ones.
Eldritch gift (passive) the next wave will be converted to eldritch cultists.
Maybe the second ability could be switched to a Buff or something, if the cultist mechanic is too difficult to implement. Something like raising the HP or the luck of all towers by 5 %