Do I still try to redeem cumulative upkeep? Maybe.

I think the timing will be very confusing in practice. That state trigger doesn't go on the stack until after the upkeep trigger finishes resolving, so you don't get around paying for the third counter, but I can see people screwing that up a lot

I thought about making it an activated ability:

> Remove all age counters from ~: If at least three age counters were removed this way, transform ~. Activate only as a sorcery.

Maybe a trigger at the beginning of the draw step or (first) main phase?

I wouldn't have bothered to point this out because it's just a technicality. But since dude called out the upkeep problem, I might as well point this out too.

The way the trigger is set up, it would cause the game to immediately end in a tie. That's because the ability would trigger and go on the stack, then while we wait for it to resolve, it would trigger and go on the stack, then while we wait for it to resolve, it would trigger and go on the stack...

It's a state trigger. They have a special section in the rules explicitly preventing the mentioned loop. It's why existing cards like Emperor Crocodile work without causing a loop.

Ah. Then nevermind and carry on.

I actually decided it is more important to add clarity regarding the triggered ability on the back - which you usually don't get to benefit from despite everything, including transformation, happening during upkeep.

Changing to precombat main phase trigger.