msem-instigator

Whenever a creature you control enters, Timid Thunderhorn gets +X/+X until end of turn, where X is that creature's power.

Enchant creature
Enchanted creature gets +3/+3 and has trample.

Towering Boughs enters tapped.
{T}: Add {R} or {G}.
{3}{R}{G}: Until end of turn, Towering Boughs becomes a 6/6 red and green Treefolk creature with with trample and “Whenever this creature attacks or blocks, torment yourself.” It's still a land. (To torment yourself, lose 3 life unless you discard a card or sacrifice a nonland permanent.)

Whenever another nontoken creature you control enters, that creature gains haste until end of turn. Then Tremor Seer deals 1 damage to any target.

I — Create a 1/1 red Hound creature token.
II — Create a 4/4 green Rhino Warrior creature token with trample.
III — You may have two target creatures you control fight. If you do and exactly one survives, put four +1/+1 counters on that creature.

Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)
{4}{R}{G}: Twinblade Paragon gains double strike until end of turn.

Flying
When Tyrant of Tributes enters, target opponent sacrifices X permanents, where X is half the number of permanents they control, rounded up. You gain X life.

Trample, haste
When Tyrants of Bundan enters, tap all lands target player controls. They don't untap during their controller's next untap step.

Whenever a land becomes tapped, its controller sacrifices it and creates a Treasure token.

Flying, haste
Venwyn, the Dragon's Fang can't block.
At the beginning of combat on your turn, you may pay {1}{R/G}. If you do, create a token that's a copy of target creature you control with mana value 3 or less, except it's not legendary and has haste. Exile that token at end of combat.

{T}: Add {C}.
{T}, Pay 1 life: Add {R} or {G}.

You may play Vibrant Sandbar from your graveyard as long as seven or more cards are in your graveyard.
Vibrant Sandbar enters tapped.
{T}: Add {R} or {G}.
Cycling {1}{R}{G} ({1}{R}{G}, Discard this card: Draw a card.)

Create a token that's a copy of target creature or land you control, except it has haste and “At the beginning of the end step, exile this permanent.” If a land you control was targeted this way, create two of those tokens instead.

Reach
Wanderlust — Voliv Skyhunter gets +2/+0 and has first strike as long as you control four or more differently named lands.

{2}{R}: Creatures you control get +1/+0 until end of turn.
{1}{G}: Creatures you control gain trample until end of turn.

You may exert Wiedfree Berserker as it attacks. When you do, target creature can't block this turn. (An exerted creature won't untap during your next untap step.)
If exerting a creature you control causes a triggered ability of a permanent you control to trigger, that ability triggers another time.

Whenever a player casts an instant or sorcery spell, Wiedfree Roughrider deals 2 damage to that player.
Whenever Wiedfree Roughrider attacks, you may pay {X}. When you do, destroy target noncreature, nonland permanent with mana value X.

Wild Peak enters tapped unless you have 15 or less life.
{T}: Add {R} or {G}.

Wild Ravine enters tapped unless you control two or more red and/or green permanents.
{T}: Add {R} or {G}.

Whenever a creature blocks Wildborn Courtesan, draw a card.
{R}{R}: Untap target creature an opponent controls. That creature blocks Wildborn Courtesan this turn if able.

At the beginning of combat on your turn, if you control a creature with power 4 or greater, put a +1/+1 counter on Wilderkin Zealot.
{R}{G}: Target creature gains trample until end of turn.

{2}{R/G}: Wildershrine Warden gets +2/+2 until end of turn. You may have it assign its combat damage this turn as though it weren't blocked. Activate only once each turn.

Wildfire Elemental has frenzy 4 as long as you control no other creatures. (Whenever this creature attacks and isn't blocked, it gets +4/+0 until end of turn.)
Wildfire Elemental has frenzy 4 as long as you have no cards in hand.

Wildrune Thicket enters tapped unless you have two or more opponents.
{T}: Add {R} or {G}.

Archive 3 (As this enters, shuffle the top three cards of your main library into a new face up library. Sacrifice this after the archived library is empty.)
You may cast the top card of the archived library. Whenever you do, copy that spell. You may choose new targets for the copy.