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.

Rabid Wolverines

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

Assembled Alphas

Whenever Assembled Alphas blocks or becomes blocked by a creature, Assembled Alphas deals 3 damage to that creature and 3 damage to that creature's controller.

Gang of Elk

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

Barrow-Blade

Equipped creature gets +1/+1.
Whenever equipped creature blocks or becomes blocked by a creature, that creature loses all abilities until end of turn.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Lost Vale

(Transforms from Dowsing Dagger.)
{T}: Add three mana of any one color.

Dowsing Dagger

When Dowsing Dagger enters, target opponent creates two 0/2 green Plant creature tokens with defender.
Equipped creature gets +2/+1.
Whenever equipped creature deals combat damage to a player, you may transform Dowsing Dagger.
Equip {2}

Dowsing Dagger // Lost Vale

Jetmir, Nexus of Revels

Creatures you control get +1/+0 and have vigilance as long as you control three or more creatures.
Creatures you control also get +1/+0 and have trample as long as you control six or more creatures.
Creatures you control also get +1/+0 and have double strike as long as you control nine or more creatures.

Sylvan Offering

Choose an opponent. You and that player each create an X/X green Treefolk creature token.
Choose an opponent. You and that player each create X 1/1 green Elf Warrior creature tokens.

Alliance of Arms

Join forces — Starting with you, each player may pay any amount of mana. Each player creates X 1/1 white Soldier creature tokens, where X is the total amount of mana paid this way.

Genesis Chamber

Whenever a nontoken creature enters, if Genesis Chamber is untapped, that creature's controller creates a 1/1 colorless Myr artifact creature token.

Gabriel Angelfire

At the beginning of your upkeep, choose flying, first strike, trample, or rampage 3. Gabriel Angelfire gains that ability until your next upkeep. (Whenever a creature with rampage 3 becomes blocked, it gets +3/+3 until end of turn for each creature blocking it beyond the first.)

Gift of the Woods

Enchant creature
Whenever enchanted creature blocks or becomes blocked, it gets +0/+3 until end of turn and you gain 1 life.

Elvish Berserker

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

Engulfing Slagwurm

Whenever Engulfing Slagwurm blocks or becomes blocked by a creature, destroy that creature. You gain life equal to that creature's toughness.

Grasping Giant

Vigilance
Whenever Grasping Giant becomes blocked by a creature, exile that creature until Grasping Giant leaves the battlefield.

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.)

Elven Warhounds

Whenever Elven Warhounds becomes blocked by a creature, put that creature on top of its owner's library.

Corrosive Ooze

Whenever Corrosive Ooze blocks or becomes blocked by an equipped creature, destroy all Equipment attached to that creature at end of combat.

General Marhault Elsdragon

Whenever a creature you control becomes blocked, it gets +3/+3 until end of turn for each creature blocking it.

Pygmy Troll

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

Godsend

Equipped creature gets +3/+3.
Whenever equipped creature blocks or becomes blocked by one or more creatures, you may exile one of those creatures.
Your opponents can't cast spells with the same name as a card exiled with Godsend.
Equip {3}

Infiltration Lens

Whenever equipped creature becomes blocked by a creature, you may draw two cards.
Equip {1}

Berserk Murlodont

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

Forbidden Orchard

{T}: Add one mana of any color.
Whenever you tap Forbidden Orchard for mana, target opponent creates a 1/1 colorless Spirit creature token.

Cave Tiger

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

Hansk, Slayer Zealot

At the beginning of your upkeep, target opponent creates three Walker tokens. (They're 2/2 black Zombie creatures.)
{T}: Hansk, Slayer Zealot deals 2 damage to target creature.
Whenever a Zombie an opponent controls dies, draw a card.

Rabid Elephant

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

Seed the Land

Whenever a land enters, its controller creates a 1/1 green Snake creature token.

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.

Ferocity

Enchant creature
Whenever enchanted creature blocks or becomes blocked, you may put a +1/+1 counter on it.