It's also NLF (
No Limits Fallacy.) to assume they can do anything without limits just because they have Toon Force.
You need feats for that character/verse's Toon Force indicating that it, for example, allows them to resist being erased from existence.
& I said "resist" despite your useage of "immune", because Immunity isn't easily achieved by our standards. Like all things, it's case by case. Feats & statements for what their Toon Force can do are what we go by.
https://vsbattles.fandom.com/wiki/Resistance#Summary
"Qualifying for Immunity is difficult, as no simple show of resistance is enough, and statements could easily be hyperbole or only apply in-verse. Immunity should only be given when the user in question entirely lacks what would normally be affected. An inorganic being, for example, has no biological components to manipulate, and an entity without a soul won't be harmed by Soul Manipulation."
To be immune to Existence Erasure for example, you'd probably need to not exist at all. Of course, that might get complicated & require some high standards met.
https://vsbattles.fandom.com/wiki/Nonexistent_Physiology
Similarly, being immune to say, Bone Manipulation, would require not having bones or such.
As for how to beat a theoretical toon, besides the fact that NLF means they may be beatable anyway.... Well, for one, Power Nullification may be an option.
It depends on what the character's Toon Force has been shown to do.
In other words, case by case, as things are often here. "It depends.".
Apologies if anyone minds such answers, or dislikes them. Hope this helps &/or is appreciable &/or interesting!