Satoru Umezawa, and Master of Cruelties

Prerequisites

• Satoru Umezawa on the battlefield
• Master of Cruelties on the battlefield
• Master of Cruelties does not have summoning sickness
• You have a creature card in hand with power one or greater
• An opponent is unable to block Master of Cruelties
• available

Steps

1. Declare Master of Cruelties as an attacker, attacking an opponent unable to block it
2. When Master of Cruelties isn't blocked, its ability triggers
3. Holding priority, activate any creature card with power one or greater in your hand's ninjutsu ability by paying and returning Master of Cruelties from the battlefield to your hand, putting the creature card onto the battlefield tapped and attacking
4. Resolve the Master of Cruelties trigger, causing the blocking opponent's life total to become one
5. Deal combat damage with the attacking creature, causing the opponent's life total to become zero or less
6. The opponent loses the game due to having zero or less life

Results

• Near-infinite lifeloss for target opponent
• Target opponent loses the game