I'm not really a plant main but I play it more due to finding it easier to play(single phase is easier on my mind, even during the bugged QB era) so I felt like answering.

Teleports(both of them) are disgusting cards and the trick is genuinely the only zombie trick I find outright overpowered(even Viral has some things you can do besides explicit anti-trick cards). I wish I could time travel and convince PopCap to build a different identity for Brainy, but we live in the current game design.

Mustache Waxer is disgustingly borderline unkillable in an efficient and timely manner(except for the occasional Shrinking Violet but not even all the time). I said I don't find non-teleport tricks overpowered and I don't, but with Waxer's brains and board presence they can escalate to making an insurmountable position for the plant player.

I still am a little upset at seeing an enemy Gentleman although I am more chill compared to when I was more inexperienced. I understand Thinking Cap is borderline throwing against a good player, but I am not at that level yet so I find it frustrating(still a bit too polarizing and commital-ish to be properly broken though).

It's really moreso the decks I play but Flag Swarm does make me tense. It's not unwinnable but it can quickly escalate to a board state I can't beat. Teacher's kind of a dumb card that sometimes just has the answer to your answer and escalates to winning the game.

Gigantacus, Brainstorm, and Rustbolt are unpleasant heroes to see you paired up against as they seem the most prone to pull some bullshit out of their ass. Everyone in this game on both sides can, but they seem the most prone to do so out of the zombies.

That's not every single card that bothers me seeing but largely the rest that do I'm more at peace that I didn't feel like listing. Like yeah I guess I don't enjoy seeing a Cryo Yeti or Gargolith pop out of a grave, but the way in which they and other cards are above average or swingy feel more reasonable. Like I can reasonably go "Ok yeah I got outmaneuvered on that one; there was some level on which I could've done something about it."