msem-instigator

Whenever a creature with a counter on it dies, create a Gold token. (It's an artifact with “Sacrifice this artifact: Add one mana of any color.”)

Create an X/X green and blue Plant creature token, where X is the number of differently named lands you control.

Harmony — Create a colorless artifact token named Lotus Petal with “{T}, Sacrifice this artifact: Add one mana of any color.”
When Bouquet Singer enters, harmonize. (Trigger up to one harmony of one permanent you control.)

Other Hounds you control get +1/+1.

Whenever Bourasan Street Watch attacks, you may pay {W}. If you do, Bourasan Street Watch gains indestructible until end of turn.

Enchant creature
Enchanted creature doesn't untap during its controller's untap step.

Gain control of target nonland permanent you don't control unless its controller has Bow or Burn deal X damage to them, where X is twice that permanent's mana value. If Bow or Burn was cast from a graveyard, repeat this process for each other nonland permanent they control.
Flashback {6}{R}{R}

You may activate Boxue and Ma'Long's loyalty abilities an additional time if you've cast two or more spells this turn.
[+1]: Scry 2.
[–2]: Exile the top two cards of your library. You may play one of them this turn. When you do, put the other card into your hand.
[–6]: Whenever you cast a spell this turn, copy it. You may choose new targets for the copy.

Untap target creature you control. It gets +4/+4 and gains reach until end of turn.

Trample
{1}{G}: Brackish Kelpie gets +2/+2 until end of turn. Activate only once each turn.

{1}, Sacrifice Brackwater Scuttler: Draw a card.

When Braenid Nomad enters, draw two cards, then discard a card.

Counter target spell. Spells its controller casts cost {2} more to cast this turn.

{1}{B}: Regenerate Brainless Ghoul. (The next time this creature would be destroyed this turn, it isn't. Instead tap it, remove all damage from it, and remove it from combat.)

If you would draw a card, instead exile the top three cards of your library face down. You may look at those cards. Put a card exiled with Brainstorming Session into its owner's hand.
{X}{X}{U}, Sacrifice Brainstorming Session: Put X cards exiled with it into their owner's hand.

Archive 5 (As this enters, shuffle the top five cards of your main library into a new face up library. Sacrifice this after the archived library is empty.)
Whenever a player discards a card, draw a card from the archived library.

[+2]: Discard a card at random. If you do, draw two cards.
[0]: Target creature's controller may pay X life. If they don't, you lose X life and gain control of it (Choose any number for X.)
[–3]: Flip a coin until you lose a flip or choose to stop flipping. For each flip you won, draw two cards and create a tapped Treasure token.

Enchant creature
When Bramble Armor enters, put a +1/+1 counter on enchanted creature.
{G}, Sacrifice Bramble Armor: Enchanted creature gains indestructible end of turn. Tap it.

When you cast this spell, copy it. You may choose new targets for the copy. (Copies keep functions.)
Draw a card.

First strike
Whenever you cast an instant or sorcery spell, if Branch Breaker dealt combat damage to a player this turn, you may sacrifice Branch Breaker. If you do, copy that spell. You may choose new targets for the copy.

Branch Prowler can't be blocked except by creatures with flying.

Erratic (When this creature dies, reveal the top four cards of your library. Put a creature card that costs less than this revealed this way onto the battlefield and the rest on the bottom of your library in any order.)

When Brand New Species enters, create a tapped 3/2 green Horror creature token.
Augmented — At the beginning of each end step, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, put a +1/+1 counter on up to one target Horror you control.