SneakSneak 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. (CR 702.190)
First strikeFirst strike is a static ability that modifies the rules for the combat damage step. (See rule 510, “Combat Damage Step.”)
If at least one attacking or blocking creature has first strike or double strike (see rule 702.4) as the combat damage step begins, the only creatures that assign combat damage in that step are those with first strike or double strike. After that step, instead of proceeding to the end of combat step, the phase gets a second combat damage step. The only creatures that assign combat damage in that step are the remaining attackers and blockers that had neither first strike nor double strike as the first combat damage step began, as well as the remaining attackers and blockers that currently have double strike. After that step, the phase proceeds to the end of combat step.
Giving first strike to a creature without it after combat damage has already been dealt in the first combat damage step won’t preclude that creature from assigning combat damage in the second combat damage step. Removing first strike from a creature after it has already dealt combat damage in the first combat damage step won’t allow it to also assign combat damage in the second combat damage step (unless the creature has double strike).
Multiple instances of first strike on the same creature are redundant. (CR 702.7)
Whenever Shark Shredder deals combat damage to a player, put up to one target creature card from that player's graveyard onto the battlefield under your control. It enters tapped and attacking that player.