Syl, Honor Spren

Indestructible
As long as Syl, Honor Spren is attached to a creature, that creatures gains +4/+0, and "When
this creature deals combat damage to a creature
an opponent controls, that creature is destroyed."
Reconfigure {3}{w} ({3}{w}: Attach to target creature
you control; or unattach from a creature. Reconfigure
only as a sorcery. While attached,
this isn't a creature.)