Myself and three friends recently got this trophy and it was the last one I needed before the platinum.
After several attempts and some online digging we found the best map was Sharkbite shores & the best garden was the far side over by the sea. You'll find an archway just in front of the garden which you can hide on top of!
We were all peashooters and you can get up on top of the archway by using the hyper ability.
Tips:
Plant a couple of healing sunflowers around the garden, if you need healing between rounds quickly hop down, run to the sunflowers & get back up top before the start of the next round.
Save your best plant pot consumables for the later rounds if possible. Save up some cash and buy plenty of sticker packs, we found the bamboo shoots and laser beans were effective, although be prepared to have to replant them as they get nailed pretty darn quick.
If you can help it try and find a balancing act between killing pirate zombies & anything that will go straight for the garden AND ALSO killing hero zombies, foot soldiers, engineers etc. We found that once or twice we got close to the end but we had neglected the garden so much it couldn't survive the later waves. Be aware that foot soldiers can use their leaps to gain access to you but can be dispatched pretty quickly as long as you spot them. You also get a great vantage point from up there so you can drop chilli bean bombs when the garden gets over-run & make good use of your gattling pea especially on the boss rounds.
On boss levels try to focus on killing everything BUT the boss first. You'll find they don't tend to attack the garden, especially the yeti & disco zombie. Again on several attempts we took the boss out first whilst the pirate zombies kept destroying the garden.
Try & keep your self revives to a minimum for the later rounds. We actually got a little lucky on the first boss round with the slots and got two money bags and only a gargantuan, and didn't use a single one of our collective 12 self revives throughout. As long as the rest of the team can survive SAVE THEM UP! You'll need them.
Finally, the extraction! On our first extraction attempt we ran straight for the zone and died en route. Best way is to defend yourselves on the archway (to be honest you can hide for the most part) and then wait until there are about 45 seconds to spare. THEN run for the zone, we found that everything was on our side of the map & after using hyper and making a dash for it with plenty of jumping making yourself harder to hit, we only came across one or two zombies on the way there. You should only have seconds to spare though so don't delay. The extraction point will be directly across the map from where you are.
Best of luck guys! It's frustrating as hell but with a few practice rounds and perhaps a little luck it's more than achievable. This is also a great way to get the heave ho trophy, as all normal zombies found here are pirate zombies.
Happy zombie hunting! :-D
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