Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Chain Reaction

Chain Reaction deals X damage to each creature, where X is the number of creatures on the battlefield.

Star of Extinction

Destroy target land. Star of Extinction deals 20 damage to each creature and each planeswalker.

Thromok the Insatiable

Devour X, where X is the number of creatures devoured this way (As this enters, you may sacrifice any number of creatures. This creature enters with X +1/+1 counters on it for each of those creatures.)

Rampaging Baloths

Trample
Landfall — Whenever a land you control enters, you may create a 4/4 green Beast creature token.

Artifact Mutation

Destroy target artifact. It can't be regenerated. Create X 1/1 green Saproling creature tokens, where X is that artifact's mana value.

Krenko, Tin Street Kingpin

Whenever Krenko, Tin Street Kingpin attacks, put a +1/+1 counter on it, then create a number of 1/1 red Goblin creature tokens equal to Krenko's power.

Avenger of Zendikar

When Avenger of Zendikar enters, create a 0/1 green Plant creature token for each land you control.
Landfall — Whenever a land you control enters, you may put a +1/+1 counter on each Plant creature you control.

Arasta of the Endless Web

Reach
Whenever an opponent casts an instant or sorcery spell, create a 1/2 green Spider creature token with reach.