Rolling Thunder

Rolling Thunder deals X damage divided as you choose among any number of targets.

Descent of the Dragons

Destroy any number of target creatures. For each creature destroyed this way, its controller creates a 4/4 red Dragon creature token with flying.

Venerated Rotpriest

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
Whenever a creature you control becomes the target of a spell, target opponent gets a poison counter.

Soulfire Eruption

Choose any number of target creatures, planeswalkers, and/or players. For each of them, exile the top card of your library, then Soulfire Eruption deals damage equal to that card's mana value to that permanent or player. You may play the exiled cards until the end of your next turn.

Meteor Shower

Meteor Shower deals X plus 1 damage divided as you choose among any number of targets.

Shapers' Sanctuary

Whenever a creature you control becomes the target of a spell or ability an opponent controls, you may draw a card.

Volcanic Wind

Volcanic Wind deals X damage divided as you choose among any number of target creatures, where X is the number of creatures on the battlefield as you cast this spell.

Conflagrate

Conflagrate deals X damage divided as you choose among any number of targets.
Flashback—{R}{R}, Discard X cards. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Fireball

This spell costs {1} more to cast for each target beyond the first.
Fireball deals X damage divided evenly, rounded down, among any number of targets.

Setessan Tactics

Strive — This spell costs {G} more to cast for each target beyond the first.
Until end of turn, any number of target creatures each get +1/+1 and gain "{T}: This creature fights another target creature."

Blinding Flare

Strive — This spell costs {R} more to cast for each target beyond the first.
Any number of target creatures can't block this turn.

Gargos, Vicious Watcher

Vigilance
Hydra spells you cast cost {4} less to cast.
Whenever a creature you control becomes the target of a spell, Gargos, Vicious Watcher fights up to one target creature you don't control.

Ghired's Belligerence

Ghired's Belligerence deals X damage divided as you choose among any number of target creatures. Whenever a creature dealt damage this way dies this turn, populate. (Create a token that's a copy of a creature token you control.)