Steam Clean

Return target nonland permanent to its owner's hand. (Then exile this card. You may cast the creature later from exile.)

Scalding Viper

Whenever an opponent casts a spell with mana value 3 or less, this creature deals 1 damage to that player.

Scalding Viper // Steam Clean

Bloodwater Entity

Flying
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
When this creature enters, you may put target instant or sorcery card from your graveyard on top of your library.

Lutri, the Spellchaser

Companion — Each nonland card in your starting deck has a different name. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.)
Flash
When Lutri enters, if you cast it, copy target instant or sorcery spell you control. You may choose new targets for the copy.

Nivmagus Elemental

Exile an instant or sorcery spell you control: Put two +1/+1 counters on this creature. (That spell won't resolve.)

Eris, Roar of the Storm

This spell costs {2} less to cast for each different mana value among instant and sorcery cards in your graveyard.
Flying, prowess
Whenever you cast your second spell each turn, create a 4/4 red Dragon Elemental creature token with flying and prowess.

Shrewd Hatchling

This creature enters with four -1/-1 counters on it.
{U/R}: Target creature can't block this creature this turn.
Whenever you cast a blue spell, remove a -1/-1 counter from this creature.
Whenever you cast a red spell, remove a -1/-1 counter from this creature.

Crackleburr

{U/R}{U/R}, {T}, Tap two untapped red creatures you control: This creature deals 3 damage to any target.
{U/R}{U/R}, {Q}, Untap two tapped blue creatures you control: Return target creature to its owner's hand. ({Q} is the untap symbol.)