Desiccate
Sorcery (U)
Destroy all creatures with toughness 3 or less.
Illpyre is vast, yet it has no room for the weak.


Creatures that aren't sticking around for long care less than others about sorcery-speed sweep, which means it might be a bit less powerful than normal in this set. We can probably print some at uncommon without breaking limited. This should make having a large permanent army somewhat less comfortable, and players who take a copy or two of Desiccate would definitely prefer temporary creatures over more permanent ones.

Make a red sweeper of some sort. I don't care about rarity, but if it's absolutely necessary that I specify one, then make it rare.
That also means that I will assume it's rare unless specified otherwise.

Reprint Chain Reaction.

Melody of Roasting Flesh
Enchantment (R)
At the beginning of your upkeep, put a verse counter on [cardname].
, sacrifice [cardname]: [cardname] deals damage equal to the number of verse counters on it to each creature and planeswalker.

Stoke the Sun
Sorcery

You may sacrifice an enchantment with converted mana cost X rather than pay ~'s mana cost.
Choose one - ~ does X damage to each creature on the battlefield; or return ~ to your hand. If you do, at the beginning of your next pre-combat Main Phase, add to your mana pool.

Give to the sun, and the sun gives back.

Mass Delirium
Sorcery (R)
Each creature gets +X/+0 until end of turn.
Each creature deals damage to itself equal to its power.
"And one by one / Under blazing sun / By Elori's accord / To their throats put the sword." - Tome of the Sun, Songs of Worship, Song 23

Desiccate
Sorcery (U)
Destroy all creatures with toughness 3 or less.
Illpyre is vast, yet it has no room for the weak.

Solar Flare (uncommon)
Sorcery
~ deals 3 damage to each creature. Creatures dealt damage this way can't be regenerated this turn..
While it is never cold in Illpyre, the temperature is far from constant. Sometimes the heat is almost bearable, and other times it is hot enough to cook any living thing into a pile of charred bones.

Sandquake
Sorcery (R)
Sandquake deals X damage to each creature without flying and each player. If X is 5 or more, put an X/X red Hellion creature token onto the battlefield.
"The hellions are underground. Must be hot today."
—Oldest joke in Illpyre

Will of Illpyre --
Sorcery (R)

Each creatures deals damage to itself equal to its power.

It is best to be hidden midday in Illpyre. Noone can save you when everyone suffers.

Rein of Fire
Sorcery [R]
Destroy all creatures.
Each other player is dealt damage equal to the number of mountains on the field.

Missing Shazzeh's submission.

I like thatmarkguy's, except that 90% of the time it will just be cast as a board wipe for . Which is probably a little too good for red. The X is just kind of optional window dressing to sometimes kill creatures with low p:t ratios.