MTG Keyword Rules — Comprehensive Rules Glossary

Sneak is a keyword that represents a static ability that functions while the spell with sneak is on the stack. “Sneak [cost]” means “Any time you could cast an instant during your declare blockers step, you may cast this spell by paying [cost] and returning an unblocked creature you control to its owner’s hand rather than paying this spell’s mana cost.”

A permanent spell whose sneak cost was paid enters the battlefield tapped and attacking (see rule 506.3a). It will be attacking the same player, planeswalker, or battle as the creature that was returned to its owner’s hand to pay the sneak cost of the spell that became that permanent.