Thunderkin Awakener

Haste
Whenever this creature attacks, choose target Elemental creature card in your graveyard with toughness less than this creature's toughness. Return that card to the battlefield tapped and attacking. Sacrifice it at the beginning of the next end step.

Lightning Skelemental

Trample, haste
Whenever this creature deals combat damage to a player, that player discards two cards.
At the beginning of the end step, sacrifice this creature.

Spark Trooper

Trample, lifelink, haste
At the beginning of the end step, sacrifice this creature.

Bone Shards

As an additional cost to cast this spell, sacrifice a creature or discard a card.
Destroy target creature or planeswalker.

Postmortem Lunge

({B/P} can be paid with either {B} or 2 life.)
Return target creature card with mana value X from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step.

Thoughtseize

Target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

Flamekin Harbinger

When this creature enters, you may search your library for an Elemental card, reveal it, then shuffle and put that card on top.

Haggle

You may discard a card. If you do, draw a card. (Then exile this card. You may cast the creature later from exile.)

Merchant of the Vale

Merchant of the Vale // Haggle

Stitcher's Supplier

When this creature enters or dies, mill three cards. (Put the top three cards of your library into your graveyard.)

Takenuma, Abandoned Mire

{T}: Add {B}.
Channel — {3}{B}, Discard this card: Mill three cards, then return a creature or planeswalker card from your graveyard to your hand. This ability costs {1} less to activate for each legendary creature you control.

Unearth

Return target creature card with mana value 3 or less from your graveyard to the battlefield.
Cycling {2} ({2}, Discard this card: Draw a card.)

Ball Lightning

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Haste (This creature can attack and {T} as soon as it comes under your control.)
At the beginning of the end step, sacrifice this creature.