Sneak Attack [Urza's Saga] Shapeshifter Set: Legions Type: Creature —

Set: Legions Type: Creature — Elf Rare Cost: {2}{G} Flash When Caller of the Claw enters the battlefield

Set: Urza's Saga Type: Creature — Shapeshifter Rare Cost: {3}{U}{U} {U}: Untap Morphling

or planeswalker

Set: From the Vault: Relics Type: Legendary Artifact Creature — Golem Mythic Cost: {5} Whenever Karn

One razorclaw is three bears too many

Sneak Attack [Urza's Saga] Shapeshifter Set: Legions Type: Creature —Set: Urza's Saga Type: Enchantment Rare Cost: {3}{R} {R}: You may put a creature card from your hand onto the battlefield. That creature gains haste. Sacrifice the creature at the beginning of the next end step. "Nothin' beat surprise'cept rock."