Elminster

Whenever you scry, the next instant or sorcery spell you cast this turn costs {X} less to cast, where X is the number of cards looked at while scrying this way.
+2: Draw a card, then scry 2.
−3: Exile the top card of your library. Create a number of 1/1 blue Faerie Dragon creature tokens with flying equal to that card's mana value.
Elminster can be your commander.

End Hostilities

Destroy all creatures and all permanents attached to creatures.

Farewell

Choose one or more —
• Exile all artifacts.
• Exile all creatures.
• Exile all enchantments.
• Exile all graveyards.

Fell the Mighty

Destroy all creatures with power greater than target creature's power.

Shatter the Sky

Each player who controls a creature with power 4 or greater draws a card. Then destroy all creatures.

Fumigate

Destroy all creatures. You gain 1 life for each creature destroyed this way.

Catastrophe

Destroy all lands or all creatures. Creatures destroyed this way can't be regenerated.

Austere Command

Choose two —
• Destroy all artifacts.
• Destroy all enchantments.
• Destroy all creatures with mana value 3 or less.
• Destroy all creatures with mana value 4 or greater.

Rout

You may cast Rout as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)
Destroy all creatures. They can't be regenerated.

Akroma's Vengeance

Destroy all artifacts, creatures, and enchantments.
Cycling {3} ({3}, Discard this card: Draw a card.)

Cleansing Nova

Choose one —
• Destroy all creatures.
• Destroy all artifacts and enchantments.

Kirtar's Wrath

Destroy all creatures. They can't be regenerated.
Threshold — If seven or more cards are in your graveyard, instead destroy all creatures, then create two 1/1 white Spirit creature tokens with flying. Creatures destroyed this way can't be regenerated.

Cast Off

Destroy all non-Giant creatures. (Then exile this card. You may cast the creature later from exile.)

Realm-Cloaked Giant

Realm-Cloaked Giant // Cast Off

Hour of Reckoning

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Destroy all nontoken creatures.

Phyrexian Rebirth

Destroy all creatures, then create an X/X colorless Phyrexian Horror artifact creature token, where X is the number of creatures destroyed this way.