as much as I'd also love to suggest a PvZ2 plant (Caulipower or Draftodil for me personally), I'm pretty sure they're referring to just the fusions from the fusion mod.
if you look up "PvZ Fusion [plant name]", you can easily find shorts showing off the combos if you don't know the mod.
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if you look up "PvZ Fusion [plant name]", you can easily find shorts showing off the combos if you don't know the mod.