Seedling Glitch
I'm not exactly sure how this happened... But here's the story:
It's turn two, the Rustbolt played a gravestone in one lane (engineer drone zombie) and I played a Seedling in another lane. Since Seedling couldn't be hurt in any way, it got to grow into a plant... Except, it didn't.
Somehow, the Seedling turned into a Trick-Or-Treat Zombie! The game continued to get weirder from there. It was still on the side plants are played on, and I couldn't play a plant there. I could've Berry Blasted it, but I didn't. It seemed like the game didn't know what to do, and it just kind of sat there, and I didn't see it dealing any damage. Rustbolt still got the treats from its effect, however.
So you're probably wondering, can a Zombie be placed in front of it and hurt this glitched Zombie? Well, you'd be wrong. Rustbolt placed a Buckethead Zombie up front, and the Trick-Or-Treat Zombie repositioned itself back to the Zombie side, but was behind the Buckethead as if it had Team-Up. Yet, it still refused to attack. But when the Buckethead attacked, its animation played like normal but I didn't take damage. It must've thought the Trick-Or-Treat Zombie was still on the Plant side, and disappeared afterwards without an animation. So the Buckethead still hit the Trick-Or-Treat Zombie, and said Zombie still didn't deal damage. The game had returned back to normal for the most part, but the Buckethead was still out of place. Obviously I lost because I was too busy experimenting, and (unregrettably) lost a star.