It may be a Hyperbole or Satire. Since sawing someone's leg off is likely to be exaggerated, it may be a Hyperbole.
At the same time, depending on the context of this sentence, it may be said for the purpose of humour, so Satire.
Hyperbole seems more probable in my view. :)
I was finna sit here and do it but i’m tired so i’ll do it tomorrow morning
