I've been wanting to try out this setup for bloody ages, and I finally got around to it!  I'm to 22 flags so far, and my experience there has given me a few more clues as to this setup's strengths and weaknesses.

Bdejean mystical

Disclaimer. This is NOT my setup. This is, I believe, from baidu, and I'd like to thank Hitoridakeno for showing me how it's played.

As I noted, this is NOT my setup, though I made a minor tweak here or there.  This uses a 2-2i timing, meaning that each cob cycle, it fires 2 cobs, then fires 2 cobs and activates an Ice-shroom.  The timing for this setup is approximately:

Fire 2 cobs, then wait 18 seconds.  Start counting a short time after you make the first click to fire the first cob.

Fire another pair, and start counting to 18 seconds again, also shortly after the first cob gets fired.  ACTIVATE AN ICE-SHROOM right as the second cob hits the ground, otherwise you get major issues.

A few tips:

Football Zombies are rarely an issue, but slip-ups in timing let them get by occasionally.  If they do, Pumpkin any Gloom-shrooms in danger.

Zombonis?  Proper timing, preferably with the front land Gloom-shrooms unpumpkined, should be able to nuke 100% of them.

Gargantuars/gigas?  Just let the cobs and Gloom-shrooms take care of them.  If you're worried, use Puff-shrooms to stall them or Squash to deal some more damage.

What are the ladders for?  Imps.  The Gloom-shrooms in the back are more than enough to take care of them, and you don't want them gnawing your Pumpkins, do you?  That just means more maintenance.

And, if you're wondering why I'm missing the Lawn Mower, that was an Ice-shroom slipup.  Pogo Zombies are dangerous unless you activate that Ice-shroom.

This is the first time I've tried a laddered setup, and let me just tell you that it was slightly harder than I expected to get all those Ladders up.  It works, though!  If you're wondering, leaving the front Gloom-shrooms asleep and an absurd amount of Garlic was enough to get everything Laddered.

Dolphin Riders on the top get hindered by the Pumpkin.  (In rounds without Diggers or Catapults, you can just stockpile Ice-shrooms in the back and dig up the Ice-shroom in the water.  Dolphin Riders on the bottom get Gloomed to bits before they can nibble on those Sunflowers.