This guy has had enough experience to be called a veteran pirate of the current manga series time, no longer a rookie. The more he fought with the better and superior his opponents, the stronger he became. Brutal fights and near-death experiences he survived: Croc, Lucci, Magellan, etc. This man just do not die (plot armor, yes I am aware).
Let's see what we know about him at the moment:
- He is immune to poison, grats to Magellan for not going for the kill, so that pretty much takes care of the likes of poison attacks (the octopus in FI) or like Shinokuni.
- His buso-koka technique should be the answer for his logia opponents (e.g. Smoker, Kizaru) though am not sure if he will get burn if he buso-koka punch Sakazuki (because the FA can inflict burn as you touch to hit him) or Aokiji or a new Mera Mera user
- His Kenbunshoku reflexes should takes care of agility based attacks, therefore shooting kairoseki bullets from non-point blank range should be nullified, same goes for any specialised fast attacks (like the old Kuro and perhaps Kuma's speed)
- His Gears (Second, Third, and combination) handles almost all foes of any kinda. Gear Second ensures he is kept up to speed with very fast / agile opponents. Gear Third takes care of anyone who needs a one-massive-strength punch.
But let's fictionally say Oda let you decide how to end the protagonist's live, regardless having achieved One Piece or not. At his present state (as per manga, Dressrosa arc), how will you kill him CANONically? Bear in mind, keep your thinking as canon as possible, so to get approval from veteran OP followers.
Hope this has been entertaining. Happy weekend people!