Mockingbird

Flying
You may have Mockingbird enter as a copy of any creature on the battlefield with mana value less than or equal to the amount of mana spent to cast Mockingbird, except it's a Bird in addition to its other types and it has flying.

Island

Swiftwater Cliffs

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {U} or {R}.

Waterspout Warden

Whenever Waterspout Warden attacks, if another creature entered the battlefield under your control this turn, Waterspout Warden gains flying until end of turn.

Quaketusk Boar

Rabid Gnaw

Target creature you control gets +1/+0 until end of turn. Then it deals damage equal to its power to target creature you don't control.

Coruscation Mage

Offspring {2} (You may pay an additional {2} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
Whenever you cast a noncreature spell, this creature deals 1 damage to each opponent.

Bria, Riptide Rogue

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Other creatures you control have prowess. (If a creature has multiple instances of prowess, each triggers separately.)
Whenever you cast a noncreature spell, target creature you control can't be blocked this turn.

Alania's Pathmaker

When Alania's Pathmaker enters, exile the top card of your library. Until the end of your next turn, you may play that card.

Thieving Otter

Whenever Thieving Otter deals damage to an opponent, draw a card.

Sword of Vengeance

Equipped creature gets +2/+0 and has first strike, vigilance, trample, and haste.
Equip {3}

Mountain

Bellowing Crier

When Bellowing Crier enters, draw a card, then discard a card.

Pearl of Wisdom

This spell costs {1} less to cast if you control an Otter.
Draw two cards.

Stormcatch Mentor

Haste
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Instant and sorcery spells you cast cost {1} less to cast.

Charmed Sleep

Enchant creature
When Charmed Sleep enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Mind Spring

Flame Lash

Alania, Divergent Storm

Whenever you cast a spell, if it's the first instant spell, the first sorcery spell, or the first Otter spell other than Alania you've cast this turn, you may have target opponent draw a card. If you do, copy that spell. You may choose new targets for the copy.