msem-instigator

{4}{G}: Monstrosity 2. (If this creature isn't monstrous, put two +1/+1 counters on it and it becomes monstrous.)
When Mountain Bighorn becomes monstrous, you may have it fight target creature you don't control.

Destroy target artifact or enchantment. Its controller gains 4 life.

Destroy target creature with flying. You may put a land card from your hand onto the battlefield.

Rakkiri Archer gets +0/+1 and has reach as long as it's embattled. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Redleather Armorer gets +1/+1 as long as it's your turn.

When Rotfeeder Slime dies, you gain 2 life for each creature card in your graveyard.

Prevent all damage that would be dealt to creatures and to you this turn.

Sentinel of the Highlands has hexproof as long as it's embattled. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Whenever Steelcrusher Viking blocks or becomes blocked by a creature, destroy up to one target Aura or Equipment attached to that creature.

Whenever a creature you control becomes monstrous, draw a card.

This spell costs {X} less to cast, where X is the greatest power among creatures you control.
Trample

Dominance — When Viking Packleader enters, create a 2/2 green Wolf creature token if you control the creature with the greatest power or tied for the greatest power.

When Vitality Reclaimer enters, you may return target permanent card from your graveyard to your hand.

Vigilance
Whenever Warfield Excavator attacks, you may exile target card from a graveyard.
Warfield Excavator gets +1/+1 for each card type among cards exiled with it.

Whenever Wild Bearmaster attacks, each other attacking creature you control gets +X/+X until end of turn, where X is Wild Bearmaster's power.

Vigilance, reach
When Winter Widow enters, you may destroy target creature with flying.

Trample
{5}{G}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)

Flash
When Ascetic of Imbalance enters, draw two cards, then discard two cards. If you discarded two cards that don't share a type, Ascetic of Imbalance deals 2 damage to any target.

When Bjarndyr Mender enters, other creatures you control get +1/+1 and gain indestructible until end of turn.

Other Warriors you control get +2/+0.
Whenever a Warrior you control dies, Bloodshed Devotee deals 1 damage to target opponent.

Deathtouch
{B}{G}, Exile Frosted Adder from your graveyard: Return another target creature card from your graveyard to your hand.

{G}{U}: Glacier Tortoise gets +5/-5 until end of turn. Activate only once each turn.

[–1]: Tap target nonland permanent. It doesn't untap during its controller's next untap step.
[–2]: Put target nonland permanent into its owner's library second from the top.
[–X]: Shuffle up to X cards from your hand into your library, then draw that many cards. You gain that much life.

Menace
Whenever Issbarren Creeper deals combat damage to a player, draw a card, then discard a card.

Target creature gets +X/+X and gains trample until end of turn, where X is the number of lands you control.
Fabled {4}{R}{G} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)