Spider-Islanders

Mayhem {1}{R} (You may cast this card from your graveyard for {1}{R} if you discarded it this turn. Timing rules still apply.)

Romantic Rendezvous

Mountain

Ominous Asylum

This land enters tapped.
{T}: Add {B} or {R}.
{4}, {T}: Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Vibrant Cityscape

{T}, Sacrifice this land: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Raging Goblinoids

Haste
Mayhem {2}{R} (You may cast this card from your graveyard for {2}{R} if you discarded it this turn. Timing rules still apply.)

Hobgoblin, Mantled Marauder

Flying, haste
Whenever you discard a card, Hobgoblin gets +2/+0 until end of turn.

Swarm, Being of Bees

Flash
Flying
Mayhem {B} (You may cast this card from your graveyard for {B} if you discarded it this turn. Timing rules still apply.)

Rocket-Powered Goblin Glider

When this Equipment enters, if it was cast from your graveyard, attach it to target creature you control.
Equipped creature gets +2/+0 and has flying and haste.
Equip {2}
Mayhem {2}

Electro's Bolt

Electro's Bolt deals 4 damage to target creature.
Mayhem {1}{R} (You may cast this card from your graveyard for {1}{R} if you discarded it this turn. Timing rules still apply.)

Pumpkin Bombardment

As an additional cost to cast this spell, discard a card or pay {2}.
Pumpkin Bombardment deals 3 damage to target creature.

Swamp

Shadow of the Goblin

Unreliable Visions — At the beginning of your first main phase, discard a card. If you do, draw a card.
Undying Vengeance — Whenever you play a land or cast a spell from anywhere other than your hand, this enchantment deals 1 damage to each opponent.

Ultimate Green Goblin

At the beginning of your upkeep, discard a card, then create a Treasure token.
Mayhem {2}{B/R} (You may cast this card from your graveyard for {2}{B/R} if you discarded it this turn. Timing rules still apply.)

Green Goblin, Revenant

Flying, deathtouch
Whenever Green Goblin attacks, discard a card. Then draw a card for each card you've discarded this turn.