(っ)ぽい is basically a suffix ("-ish"), but in very informal speech, it is sometimes used like a standalone adjective meaning それっぽい or "authentic-looking/-sounding", "believable", "plausible", etcand so on. For example,
「鳥山明みたいな絵を描いてみたよ。」「すごい、ぽい!」
あんまり、ぽくなくない?
It's not very realistic, is it?
In your case, the sticker means something like "it's becoming more authentic" or "(finally) this is like athe real onething". Looks like this is a phrase from SLAM DUNK, so I assume it was originally said with enoughsufficient context. For example, if this is said during a boring basketball game, it would be interpreted likeas "Finally, this is real basketball!". But you can use the same phrase when something different from your expectations has finally become exciting.