Glistener Elf

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Lost Leonin

Tyrranax Rex

This spell can't be countered.
Trample, ward {4}, haste
Toxic 4 (Players dealt combat damage by this creature also get four poison counters.)

Ichorclaw Myr

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever Ichorclaw Myr becomes blocked, it gets +2/+2 until end of turn.

Phyrexian Crusader

First strike, protection from red and from white
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Atraxa, Praetors' Voice

Flying, vigilance, deathtouch, lifelink
At the beginning of your end step, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)