msem-instigator

{T}: Add {G}.
{T}: Add {G}{G}. Activate only if you control an Elemental.

Trample
Whenever a creature attacks, Alpha Stag gets +2/+2 until end of turn.

Whenever Veiled Charmer attacks, target creature blocks it this turn if able.

Exile the top five cards of your library. Until end of turn, you may play any number of cards exiled this way with mana value less than or equal to the number of colors among permanents you controlled as you cast United Fervor.

Undine Coven gets +1/+1 for each other Merfolk you control.
Whenever you cast a noncreature spell, Undine Coven deals 1 damage to target player or planeswalker.

Thunder Wave deals 3 damage to target creature or planeswalker.

Haste
Heretic (Whenever you cast a spell that doesn't share a color with this creature, it gets +1/+1 until end of turn.)

Primal {1}{W}{W} (During your turn, you may cast this spell for {1}{W}{W} instead of playing a land.)
Double strike
When Sunken Slasher enters, if you didn't play a land this turn, put a +1/+1 counter on it.

Heretic (Whenever you cast a spell that doesn't share a color with this creature, it gets +1/+1 until end of turn.)
{1}{W}: You gain life equal to Sunken Outcast's power.

{W}: Target creature gains vigilance until end of turn.

Striptide deals 1 damage to target creature. Unattach all artifacts from it. It becomes red until end of turn.
Draw a card.

Heretic (Whenever you cast a spell that doesn't share a color with this creature, it gets +1/+1 until end of turn.)
When Shoring Naiad enters, if {U} was spent to cast it, you may return an instant or sorcery card from your graveyard to your hand.

Primal {3}{U}{U} (During your turn, you may cast this spell for {3}{U}{U} instead of playing a land.)
Draw a card for each land you control, then discard that many cards unless this spell was cast for its primal cost.

{2}{W}, {T}: Target creature gets +2/+2 and gains first strike until end of turn.

Whenever one or more nontoken Merfolk you control attack, create a 2/1 red Merfolk creature token.

Up to three target creatures each get +1/+1 until end of turn.

Enchant creature
Enchanted creature gets +3/+0 and has menace.
Whenever enchanted creature deals combat damage to a player, discard a card, then draw a card.

River's Wrath deals 2 damage to any target. If you've been dealt damage this turn, River's Wrath deals 4 damage instead.

Primal {R} (During your turn, you may cast this spell for {R} instead of playing a land.)
Target creature gets +4/+0 and gains trample until end of turn.

Whenever you cast a spell that doesn't share a color with Raloran Adept, you may switch target creature's power and toughness until end of turn.

Menace, haste

Whenever you cast a red spell, target creature gets +1/+0 and gains haste until end of turn.

Whenever a noncreature permanent enters, Petaldiver deals 1 damage to that permanent's controller.

As an additional cost to cast this spell, discard a card.
Draw two cards.

Overkill deals 4 damage to any target that was dealt damage this turn.