Deathtouch
The first instant or sorcery spell you cast each turn has casualty 2. (As you cast that spell, you may sacrifice a creature with power 2 or greater. When you do, copy the spell and you may choose new targets for the copy.)
(29/04/2022)
If you pay the casualty cost of a spell, the copy will resolve before the original spell.
(29/04/2022)
You may sacrifice only one creature to pay a spell's casualty cost, and you copy the spell only once.
(29/04/2022)
Casualty N means “As an additional cost to cast this spell, you may sacrifice a creature with power N or greater.” and “When you cast this spell, if a casualty cost was paid for it, copy it. If the spell has any targets, you may choose new targets for the copy.”
(29/04/2022)
The copy of the spell is created on the stack, so it's not “cast.” Abilities that trigger when a player casts a spell won't trigger.
