Tetravus, Sage of Hours, and Cathars' Crusade

Prerequisites

• Tetravus on the battlefield
• Sage of Hours on the battlefield
• Cathars' Crusade on the battlefield
• Tetravus has at least five +1/+1 counters on it

Steps

1. At the beginning of your upkeep, Tetravus' first and second abilities trigger
2. Resolve Tetravus' second ability, choosing not to exile any tokens
3. Resolve Tetravus' first ability, causing you to remove five +1/+1 counters from Tetravus to create five 1/1 Tetravite creature tokens
4. The Tetravites enter the battlefield, triggering Cathars' Crusade five times, putting five +1/+1 counters on each creature you control
5. Activate Sage of Hours by removing all +1/+1 counters from it, causing you to take at least one extra turn after this one
6. Repeat each turn

Results

• Infinite turns