msem-instigator

Each creature you control enters with an additional +1/+1 counter on it.
When Training Sim enters, create a Function token with “Target creature you control fights target creature you don't control.” (It's an enchantment. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)

Target creature gets -2/-2 until end of turn.
{3}{B}{B}, Exile Ominous Wind from your graveyard: Each creature gets -2/-2 until end of turn. Activate only as a sorcery.

Flying
Herald of Oblivion enters with X -1/-1 counters on it, where X is your life total.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Sacrifice Bonetooth Darter: Counter target instant, planeswalker, or sorcery spell unless its controller pays {1}.

Kicker {U} (You may pay an additional {U} as you cast this spell.)
Counter target spell. If this spell was kicked, look at the top three cards of your library, then put them back in any order.

Target creature gets +1/+1 for each creature you control and gains flying and vigilance until end of turn.

Put target land card from a graveyard onto the battlefield under your control.

Flying, vigilance

Enchant player
When Curse of Scuttling Thoughts enters, create a 0/3 blue Crab creature token with “{T}: Target player mills a card.”
If enchanted player would mill one or more cards, they mill twice that many cards instead.

Target creature you control gets +3/+3 and gains trample until end of turn. Other creatures you control gain trample until end of turn.

Enchant land
Enchanted land has “{T}: Target creature gets -1/-1 until end of turn. Activate only as a sorcery.”

Armed — Beragnian Blacksmith can't attack unless it's equipped.
When Beragnian Blacksmith enters, you may pay {2}. If you do, arm it. (Create a colorless Equipment artifact token with “Equipped creature gets +1/+0” and equip {2}, then attach it to this creature.)

Target creature gets -2/-2 until end of turn.
Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, return up to one target enchantment card from your graveyard to your hand.

Play with the top card of your library revealed.
You may cast Elemental spells from the top of your library.

You have no maximum hand size.
Whenever a player casts a spell, put a +1/+1 counter on Humar.
At the beginning of your upkeep, target player draws cards equal to Humar's power.

Other Shaman creatures you control get +1/+0.
Revive {4}{G}{G} ({4}{G}{G}, Exile this card from your graveyard: Create a token that's a copy of it except it has no mana cost. Revive only as a sorcery.)

Haste
Whenever two or more creatures you control deal combat damage to a player, tap those creatures, then gain control of target creature you don't control until end of turn. Untap that creature. It gains haste until end of turn. After this phase, there's an additional combat phase.

Counter target creature spell. Create a 2/2 blue Illusion creature token.

When Crackling Palm Ascetic enters, target creature gains double strike until end of turn.

Creatures you control get +1/+0 and gain haste until end of turn.

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

Whenever you cast a spell, if it isn't your main phase, create a 1/1 white Monk creature token, then creatures you control get +1/+1 until end of turn.

Primal {W} (During your turn, you may cast this spell for {W} instead of playing a land.)
When Captured Paletusk enters, you may search your library for a basic Plains card, put it onto the battlefield tapped, then shuffle. You gain 2 life. Then sacrifice Captured Paletusk if it was cast for its primal cost.

{U}: Sea Strider gets +1/-1 until end of turn.
{U}: Sea Strider gets -1/+1 until end of turn.

Search your library for a Dragon card, reveal it, put it into your hand, then shuffle. It deals damage equal to its power to you.