Practice Room. Free to Play (F2P) strategy with Dusk Lobber as primary damage dealer helped by Shrinking Violet, Winter Melon for slowing movement, and Spear-mint to counter Hamster Balls (also helps to distract Gargantuar). Plant Food is mostly used on Shrinking Violet, and sometimes on Spear-mint to break Hamster Balls.
I want to note that when I just tried this in actual Battlez, the zombies seem tougher and at the start may make it past several columns of front-line plants. It's beyond me why the developers would make the practice mode different.
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