Pygmy Troll

Whenever this creature becomes blocked by a creature, this creature gets +1/+1 until end of turn.
{G}: Regenerate this creature.

Horrible Hordes

Rampage 1 (Whenever this creature becomes blocked, it gets +1/+1 until end of turn for each creature blocking it beyond the first.)

Craterhoof Behemoth

Haste
When this creature enters, creatures you control gain trample and get +X/+X until end of turn, where X is the number of creatures you control.

Sparring Golem

Whenever this creature becomes blocked, it gets +1/+1 until end of turn for each creature blocking it.

Berserk Murlodont

Whenever a Beast becomes blocked, it gets +1/+1 until end of turn for each creature blocking it.

Gnarlid Colony

Kicker {2}{G} (You may pay an additional {2}{G} as you cast this spell.)
If this creature was kicked, it enters with two +1/+1 counters on it.
Each creature you control with a +1/+1 counter on it has trample. (It can deal excess combat damage to the player or planeswalker it's attacking.)

Baloth Pup

This creature has trample as long as it has a +1/+1 counter on it.

Aura Gnarlid

Creatures with power less than this creature's power can't block it.
This creature gets +1/+1 for each Aura on the battlefield.

Beastmaster's Magemark

Enchant creature
Creatures you control that are enchanted get +1/+1.
Whenever a creature you control that's enchanted becomes blocked, it gets +1/+1 until end of turn for each creature blocking it.

Craw Giant

Trample
Rampage 2 (Whenever this creature becomes blocked, it gets +2/+2 until end of turn for each creature blocking it beyond the first.)

Cave Tiger

Whenever this creature becomes blocked by a creature, this creature gets +1/+1 until end of turn.

Aerathi Berserker

Rampage 3 (Whenever this creature becomes blocked, it gets +3/+3 until end of turn for each creature blocking it beyond the first.)

Fangren Firstborn

Whenever this creature attacks, put a +1/+1 counter on each attacking creature.

Gorilla Berserkers

Trample; rampage 2 (Whenever this creature becomes blocked, it gets +2/+2 until end of turn for each creature blocking it beyond the first.)
This creature can't be blocked except by three or more creatures.

Cliffrunner Behemoth

This creature has haste as long as you control a red permanent.
This creature has lifelink as long as you control a white permanent.

Frost Giant

Rampage 2 (Whenever this creature becomes blocked, it gets +2/+2 until end of turn for each creature blocking it beyond the first.)

Rabid Wolverines

Marhault Elsdragon

Varchild's War-Riders

Cumulative upkeep—Have an opponent create a 1/1 red Survivor creature token. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Trample; rampage 1 (Whenever this creature becomes blocked, it gets +1/+1 until end of turn for each creature blocking it beyond the first.)

Wolverine Pack

Teeka's Dragon

Flying; trample; rampage 4 (Whenever this creature becomes blocked, it gets +4/+4 until end of turn for each creature blocking it beyond the first.)

Branchsnap Lorian

Trample
Morph {G} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Elder Gargaroth

Vigilance, reach, trample
Whenever this creature attacks or blocks, choose one —
• Create a 3/3 green Beast creature token.
• You gain 3 life.
• Draw a card.

Barreling Attack

Target creature gains trample until end of turn. When that creature becomes blocked this turn, it gets +1/+1 until end of turn for each creature blocking it.

Elvish Berserker

Neyith of the Dire Hunt

Whenever one or more creatures you control fight or become blocked, draw a card.
At the beginning of combat on your turn, you may pay {2}{R/G}. If you do, double target creature's power until end of turn. That creature must be blocked this combat if able. ({R/G} can be paid with either {R} or {G}.)

Copperhoof Vorrac

This creature gets +1/+1 for each untapped permanent your opponents control.

Gang of Elk

Whenever this creature becomes blocked, it gets +2/+2 until end of turn for each creature blocking it.

Balduvian War-Makers

Haste
Rampage 1 (Whenever this creature becomes blocked, it gets +1/+1 until end of turn for each creature blocking it beyond the first.)

Rabid Elephant

Bulette

At the beginning of your end step, if a creature died this turn, put a +1/+1 counter on this creature.

Viashino Weaponsmith

Whenever this creature becomes blocked by a creature, this creature gets +2/+2 until end of turn.

Retaliation

Creatures you control have "Whenever this creature becomes blocked by a creature, this creature gets +1/+1 until end of turn."