Can't translate this sentence:
しんネタ どらにゃんこを マスター!
Can be also たね (kana reversed).
Context:
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Sign up to join this communityAs you mentioned, ネタ is the 倒語/anadrome (reverse-ordered word) of 種{たね}/seed. It is usually used to refer to the source of a joke, comedy sketch, or an impersonation. しんネタ is 新ネタ, new ネタ.
I believe it is pretty common in the context of 漫才 where people talk about how a joke makes fun of a celebrity or a well-known event. You linked a meme in your question and in memes the idea is the same: the source or material for a joke.
どらにゃんこ is a play on どら焼き.