msem-instigator

Bloodprice {U} (You may cast this card by sacrificing a creature and paying its bloodprice.)
Counter target spell unless its controller pays {4}.

When Landbirth Elemental enters, you may search your library for a basic land card, reveal it, put it into your hand, then shuffle.

When Halskrow Street Scavenger enters, if a creature died under your control this turn, create a 2/2 green Wolf creature token.

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)

When Prophetic Prismite enters, draw a card.
{2}: Add one mana of any color.

Whenever Goblin Raidleader attacks, create a 1/1 red Goblin creature token that's tapped and attacking.
{1}{R}: Other Goblins you control get +1/+0 until end of turn.

Primal {1}{B} (During your turn, you may cast this spell for {1}{B} instead of playing a land.)
Each opponent discards two cards.

When Shojiro, the Wavewaker enters, submerge up to eight target creatures your opponents control. (To submerge a card, exile it, then put it on the battlefield face down under its owner's control as a 2/2 creature.)

Enchant creature
Enchanted creature can't block or be blocked.
{U}: Enchanted creature gets +1/+0 or -1/-0 until end of turn.

Rilken Forcefield Keeper gets +1/+1 for each enchantment you control.
Sacrifice Rilken Forcefield Keeper: Exile target permanent you control. Return that card to the battlefield under your control at the beginning of the next end step.

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

Protection from tokens
[+1]: Each player may draw a card. For each opponent that does, you gain 1 life and create a 1/1 colorless Construct Actor creature token
[–2]: Each player sacrifices a creature. Create a token that's a copy of a creature sacrificed this way.
[–7]: Until end of turn, each creature you control becomes a 6/6 black Horror creature with trample, menace, and lifelink.

Enchant creature
Enchanted creature gets +1/+1.
When enchanted creature dies, you may exile it. If you do, return target creature card from your graveyard to the battlefield.

At the beginning of each player's end step, that player chooses from among nonland permanents they control an artifact, a creature, an enchantment, and a planeswalker, then sacrifices the rest.

You draw X cards and you lose X life, where X is the number of different names among land cards in your graveyard.

Sycophantic Aristocrat gets +2/+1 as long as you control another Noble.

Whenever you activate a loyalty ability of Reyhsia, Truth Chaser, you may exile a card from your hand. If you do, draw a card.
[+2]: Each player exiles up to two cards from their hand, then draws that many cards.
[0]: Until end of turn, you may play a card exiled with Reyhsia and you may spend mana as though it were mana of any color to cast that spell.
[–10]: Each player exiles all but the bottom card of their library and may play cards they own exiled this way until the end of their next turn.

Trample
Overgrown Spellroot gets +1/+1 for each creature token you control.
When Overgrown Spellroot enters, create four 1/1 black Worm creature tokens.

Create a 4/4 red Dragon creature token with flying. Then that token deals 4 damage to each other creature and each opponent.

Counter target spell. If that spell is countered this way, put it into its owner's hand instead of into that player's graveyard. That player mills three cards.

When Doomed Traveler dies, create a 1/1 white Spirit creature token with flying.

Encourage ({T}: Another target creature you control gets +1/+1 until end of turn. Encourage only as a sorcery.)
Whenever Eos Beseecher encourages a creature, look at the top card of your library. If it's a creature card with power 2 or less, you may reveal it and put it into your hand.

Flash
When Dehmi, Origin Seeker enters, counter target spell an opponent controls unless that spell's controller has you create X 1/1 red Elemental creature tokens, where X is that spell's mana value.

Desert Temple enters tapped.
As Desert Temple enters, an opponent of your choice chooses Oasis or Desiccation.
• Oasis — {T}: Add one mana of any color.
• Desiccation — {T}: Add {C}{C}. You lose 1 life.