msem-instigator

Swiftstep Cliffdweller has haste as long as you control another Goblin.

Swallowed by the Earth deals 4 damage to target creature. Destroy all Equipment attached to that creature.

Target creature gets +2/+2 and gains trample until end of turn.
Reprise {2}{R} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)

{T}, Sacrifice an artifact: Add {R}{R}{R}.

Prowess
Whenever you cast a noncreature spell, you may choose target permanent with one or more time counters on it, then put a time counter on it or remove a time counter from it.

Roggar's Gambit deals 2 damage to any target.
Reprise {1}{R} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)
Damage dealt by sources reprising Roggar's Gambit can't be prevented.

Roggar's Frenzy deals 3 damage to any target.
{2}{R}, Exile Roggar's Frenzy from your graveyard: Create two tapped 1/1 red Elemental creature tokens.

Mill three cards. Pyromancer's Fury deals damage to any target equal to the number of instant and sorcery cards in your graveyard.

Meteor Volley deals 3 damage to each creature.
Reprise {4}{R}{R} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)

Armed — Merciless Brute gets +2/+2 as long as it's equipped.

Vanishing 1 (This creature enters with a time counter on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
Whenever a creature you control deals combat damage to a player, put a time counter on Lavacore Elemental.

Koth's Retaliation deals 4 damage to target creature. When that creature dies this turn, exile its controller's graveyard.

[+1]: Search your library for a Mountain card, reveal it, put it into your hand, then shuffle.
[–2]: Koth, One True Hero deals damage to target creature equal to the number of Mountains you control.
[–7]: Create X 3/1 red Elemental creature tokens with trample and haste, where X is the number of Mountains you control.

Cast Khalizors' Last Stand only during your postcombat main phase.
Gain control of target creature until end of turn. Untap all creatures you control. They gain haste until end of turn. After this phase, there is an additional combat phase followed by an additional main phase.

Enchant creature
Enchanted creature gets +3/+0 and has haste and menace.

Destroy target artifact.
Reprise {R} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)

Armed — Whenever Hordedriver Enthusiast attacks, if it's equipped, creatures you control get +1/+0 and gain trample until end of turn.

When Goblin Twinblades enters, create a 1/1 red Goblin creature token.

Gain control of target creature until end of turn. Untap that creature. Until end of turn, it gets +1/+0 and gains haste.

Search your library for an Equipment card, reveal it, put it into your hand, then shuffle.

Attacking creatures you control have “{R}: This creature gets +1/+0 until end of turn.”
Armed — Whenever Forgeborn Barbarian attacks, add {R} for each equipped creature you control.

Vanishing 3 (This creature enters with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
When Fickleflame Summon enters or leaves the battlefield, draw a card, then discard a card.

At the beginning of your upkeep, exile the top card of your library. Until end of turn, you may play that card if it's an instant or sorcery card.

Until end of turn, whenever you cast an instant or sorcery spell, you may discard a card. If you do, draw a card.

Prowess
Vanishing 2 (This creature enters with two time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)