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

Infinite turns

Tetravus

Sage of Hours

Cathars' Crusade

At the beginning of your upkeep, Tetravus triggers twice.
If Tetravus has fewer than four +1/+1 counters on it, follow these steps; otherwise, skip to step 7.
Resolve the token making ability, removing all +1/+1 counters from Tetravus and creating twice that many Tetravite tokens.
Resolve the token exiling ability, exiling those tokens and putting twice that many +1/+1 counters on Tetravus.
Move to your next turn.
At the beginning of your upkeep, Tetravus triggers twice.
Resolve the token making ability, removing at least four +1/+1 counters and creating at least eight Tetravite tokens.
Activate Time Sieve by sacrificing five Tetravite tokens, granting you an extra turn after this one.
Resolve the token exiling ability, exiling at least three Tetravite tokens.
Repeat from step 5.

Combos with "Tetravus"