When Conclave Sledge-Captain enters the battlefield, its backup ability triggers three times.
Resolve the first trigger, putting a +1/+1 counter on the creature with power two or greater, and causing it to gain the printed abilities until end of turn.
Simic Ascendancy's first ability triggers, putting a growth counter on it.
Repeat from step 3 for each remaining trigger.
Deal combat damage with the creature that was targeted in step 3, triggering the creature's ability three times.
Resolve the first trigger, putting a number of +1/+1 counters on the creature equal to the damage dealt.
Simic Ascendancy's first ability triggers, putting that many growth counters on it.
Repeat from step 7 for each remaining trigger.
At the beginning of your next upkeep, Simic Ascendancy's second ability triggers, causing you to win the game.
Results
Win the game at the beginning of your next upkeep.