Necro, Friendly Necromancer

When Necro, Friendly Necromancer enters the battlefield, you may pay {1}{b} any number of
times. When you pay this cost one or more times,
create that many 1/1 black Skeleton creature tokens.
Zombies and other Skeletons you control get
+1/+1.
{u}{u}{b}{b}: Return Necro from your graveyard
to the battlefield tapped. Activate this ability only
once each turn.