Whenever Shredder attacks a player, for each other opponent, create a token that's a copy of Shredder tapped and attacking that player, except it isn't legendary. Sacrifice those tokens at end of combat.
Whenever Shredder deals combat damage to a player, that player loses half their life, rounded up.
Cast Shredder, swing at a player, and create attacking copies aimed at every other opponent so all three lose half their life in one combat step. Repeat each turn to chunk life totals into oblivion, then close with damage doublers, extra combats, or evasion. Protect Shredder, keep him connecting, and lean on the exponential life-loss to set up a finishing blow.
Halves multiple opponents' life totals simultaneously every combat, accelerating any kill
Token copies trigger the damage clause independently, hitting the whole table at once
Mono-black gives deep access to tutors, removal, recursion, and reanimation
Naturally pairs with evasion, double strike, and extra-combat effects for explosive turns
Ninjutsu synergy lets you swap him in cheaply and dodge sorcery-speed removal
Halving rounds up and never goes below the last point, so you still need real damage or a finisher to close
Relies on connecting in combat—blockers, fog, and damage prevention shut him down
Removal-heavy tables can repeatedly answer a 5-mana commander, taxing your resources
Mono-black struggles with enchantment/artifact removal and flying defense
Token copies are sacrificed at end of combat, so no lingering board presence