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.)
You and permanents you control gain hexproof until end of turn. (You and they can't be the targets of spells or abilities your opponents control.)
When Lazotep Reaver enters the battlefield, 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.)
Whenever a creature you control dies, draw a card.
[+1]: Create a 2/2 black Zombie creature token.
[−4]: Each player sacrifices two creatures.
[−9]: Each opponent chooses a permanent they control of each permanent type and sacrifices the rest.
When Martyr for the Cause dies, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Menace
When Massacre Girl enters the battlefield, each other creature gets -1/-1 until end of turn. Whenever a creature dies this turn, each creature other than Massacre Girl gets -1/-1 until end of turn.
Flying
When Merfolk Skydiver enters the battlefield, put a +1/+1 counter on target creature you control.
: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Trample
Whenever you cast a noncreature spell, Mizzium Tank becomes an artifact creature and gets +1/+1 until end of turn.
Crew 1 (Tap any number of creatures you control with total power 1 or more: This Vehicle becomes an artifact creature until end of turn.)
: Add .
: Mobilized District becomes a 3/3 Citizen creature with vigilance until end of turn. It's still a land. This ability costs less to activate for each legendary creature and planeswalker you control.