Hardened Scales

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

Burrowguard Mentor

Trample
Burrowguard Mentor's power and toughness are each equal to the number of creatures you control.

Beast Whisperer

Whenever you cast a creature spell, draw a card.

Hare Raising

Target creature you control gains vigilance and gets +X/+X until end of turn, where X is the number of creatures you control.

Pollen-Shield Hare

Pollen-Shield Hare // Hare Raising

Birds of Paradise

Hare Apparent

When this creature enters, create a number of 1/1 white Rabbit creature tokens equal to the number of other creatures you control named Hare Apparent.
A deck can have any number of cards named Hare Apparent.

Regal Bunnicorn

Regal Bunnicorn's power and toughness are each equal to the number of nonland permanents you control.

Byrke, Long Ear of the Law

Vigilance
When Byrke enters, put a +1/+1 counter on each of up to two target creatures.
Whenever a creature you control with a +1/+1 counter on it attacks, double the number of +1/+1 counters on it.

Cathars' Crusade

Whenever a creature you control enters, put a +1/+1 counter on each creature you control.