Grafted Exoskeleton

Equipped creature gets +2/+2 and has infect. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever Grafted Exoskeleton becomes unattached from a permanent, sacrifice that permanent.
Equip {2}

Imodane, the Pyrohammer

Whenever an instant or sorcery spell you control that targets only a single creature deals damage to that creature, Imodane deals that much damage to each opponent.

Flame Slash

Flame Slash deals 4 damage to target creature.

Ruby Medallion

Red spells you cast cost {1} less to cast.

Scorching Shot

Scorching Shot deals 5 damage to target creature.

Solphim, Mayhem Dominus

If a source you control would deal noncombat damage to an opponent or a permanent an opponent controls, it deals double that damage to that player or permanent instead.
{1}{R/P}{R/P}, Discard two cards: Put an indestructible counter on Solphim, Mayhem Dominus. ({R/P} can be paid with either {R} or 2 life.)

Magus of the Wheel

{1}{R}, {T}, Sacrifice Magus of the Wheel: Each player discards their hand, then draws seven cards.

Jeweled Lotus

{T}, Sacrifice Jeweled Lotus: Add three mana of any one color. Spend this mana only to cast your commander.

Hell to Pay

Hell to Pay deals X damage to target creature. Create a number of tapped Treasure tokens equal to the amount of excess damage dealt to that creature this way.

Valakut, the Molten Pinnacle

Valakut, the Molten Pinnacle enters tapped.
Whenever a Mountain you control enters, if you control at least five other Mountains, you may have Valakut, the Molten Pinnacle deal 3 damage to any target.
{T}: Add {R}.

Repercussion

Whenever a creature is dealt damage, Repercussion deals that much damage to that creature's controller.

Rodeo Pyromancers

Whenever you cast your first spell each turn, add {R}{R}.

Sensei's Divining Top

{1}: Look at the top three cards of your library, then put them back in any order.
{T}: Draw a card, then put Sensei's Divining Top on top of its owner's library.

Crackle with Power

Crackle with Power deals five times X damage to each of up to X targets.

Dictate of the Twin Gods

Flash
If a source would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Extraplanar Lens

Imprint — When Extraplanar Lens enters, you may exile target land you control.
Whenever a land with the same name as the exiled card is tapped for mana, its controller adds one mana of any type that land produced.

Neheb, the Eternal

Afflict 3 (Whenever this creature becomes blocked, defending player loses 3 life.)
At the beginning of each of your postcombat main phases, add {R} for each 1 life your opponents have lost this turn.

Ancient Tomb

{T}: Add {C}{C}. Ancient Tomb deals 2 damage to you.

Deflecting Swat

If you control a commander, you may cast this spell without paying its mana cost.
You may choose new targets for target spell or ability.