Luna, Moonlight Hostess

Zombies you control have swampwalk. (This
creature can't be blocked as long as defending player controls a Swamp.)
Each land is a Swamp in addition to its other
land types.
At the beginning of your end step, amass 1. (Put
a +1/+1 counter on an Army you control. If you don't control one, create a 0/0 black Zombie Army creature
token first.)