WB Ninjas is the obvious home, and Karai sits at the apex of that archetype's curve: a strong P1P2 to P1P4 in any pack without a removal spell or a top-end legend. Hardcasting her at three for a 3/3 that returns a creature card to hand on connect is the floor, and that floor is maindeck in any black deck that can cast her. She buys back a body every time she lands damage, the kind of grinding advantage a medium-speed format rewards.
Sneak is what lifts her into the early band. With fifty-nine Sneak cards in the set, the enabler half (an unblocked attacker you can pick up at declare blockers) is functionally always online by turn four or five. Mechanized Ninja Cavalry and Foot Ninjas already want to slip through unblocked, and Karai converts that connection into a graveyard creature arriving on the battlefield as her damage resolves. The creature enters during the combat damage step, after attackers have struck, so it is a fresh body for next turn, not a second attacker this one. Even so, returning a creature to play instead of hand is the largest single tempo swing the common-and-uncommon level offers. Against a common base topping out at 2/3s and 3/2s, a 3/3 entering tapped and attacking is awkward to answer at instant speed.
Grounded for Life is the punisher, white's premier common, killing tapped creatures cheaply. Kill Karai in response to her trigger and it still resolves; the danger is the math around the Sneak line itself, where bouncing your attacker and losing Karai nets only a one-for-one. Read Sneak as a window, not a guarantee.
