Untrickable confusion

At least from what I've seen so far, "Untrickable" technically means "avoids being targeted by tricks".

You cannot affect an untrickable card with any effect status tricks (bounce, freeze) because they require targeting. 

They, however, can still be frozen or bounced with plants. It's not like they are immune to this effects, it is only that it cannot occur FROM a trick.

By the same effect, you cannot target an untrickable card with tricks that, well, require being selected (like Berry Blast, or Cakesplosion).

AoE tricks, like Weed Spray or Doom-Shroom don't work as well, but why?

I think that's because the game does the targeting for you.

Think it this way. When you play a Weed Spray, the game checks every single plant. If the plant has 2 or less attack, the game uses a "Phantom Rolling Stone" on this card. The process repeats until there are no more plants left.

Same thing with Doom-Shroom. The game checks every single zombie and cast a "Phantom Shamrocket" to those zombies. (For those who don't know, Shamrocket is the Plant version of Rocket Science), but the game can't target an untrickable card, so that's why they survive.

Knowing this, we can get an overall better idea of what can affect this card and what can't.

You can still damage it with superpowers like Power Pummel and Precision Blast because they do not target a specific zombie, but you can't affect it with things like Sunburn or Goatify.