As seen here:
From my current understand of the particle is can be used as:
な-adjectives (obviously)
Don’t (as in しぬな = don’t die)
As an order (short for なさい, like そうじしな (Clean!))
As a sentence ending particle to show doubt/surprise.
Now, how does this apply to the quote in question? Or is it something else entirely?
@Liras348 Hey! This usage of な falls into the last category you listed, “As a sentence ending particle,” which mildly asserts the speaker’s opinion/expresses emotion. I am not sure what the context of the situation is, but I am assuming that whoever the アホ that the speaker is referring to has fallen into some kind of trap or has taken the bait of something. The verb かかる can take on many meanings, but the way the speaker uses it in conjunction with “アホが,” leads me to believe it means “to be caught in” here. The full sentence could read, “アホが罠にかかったな” - “The fool fell right into (my) trap, didn’t (he).” Hope this helps!
This picture is misleading as the character is giving us the ダメ 
sign here, I was assuming a “don’t take it” context but not sure on the rest. Curious on the surrounding story now as these are fun exercises 
Ugh, that would have been a かける verb instead, oops.
@ Pushindawood is correct, the ダメ sign is part of the dude’s attack move “Thunder Cross Split Attack”.
Here’s the scene from the Anime, since I’m not sure if linking to raw manga is legal/allowed.
@ Pushindawood: Ah, perfect, thank you!
