Lets start listing pre timeskip main villains that have already returned

• Alvida (in cross guild)
• Buggy (cross guild)
• ((Arlong)) through flashback only on fishmen island
• Smoker (Punk Hazard)
• Wapol (Reverie, as king of evil drum kingdom)
• Crocodile ( cross guild)
• Bellamy
• Blackbeard
• Moria (on Fullalead island Perona tries to save him)
• Boa
• the Admirals

In sum 11 main villains returned

Villains that did not return:

• Axe Hand Morgans (his son is still at Kobys side tho)
• Kuro (but his right hand man still was present, while Garp talks about Rocks)
• Don Krieg
• Arlong
• Enel (even-tho he got his crazy moon cover story)

In sum 5 villains did not return ... Did I loose some main villains (I do not count Doflamingo, since he was only a post ts main villain) This means 11/17 = 65% of old characters did return after the timeskip to the story again, which is an ecxeptional result for a long running series imo ....

What are your general thoughts on villains returning into the story after they have been defeated. In my opinion that can get boring, if the character is not seen in a new position / context. So Crocodiles return is more boring compared to Buggys return, since Crocodile is not currently challenged and did not change his personality.

I hope some of the lesser popular characters get their chance to shine at the end, adding "depth" to seemingly unimportant characters.

For example Axe Hand Morgans still does not know he was hypnotized into believing he captured captain Kuro. Because of that hypnosis he became an arrogant high ranking officer. Bringing Axe Hand Morgans and Kuro together could lead to the revelation that his live was built on a lie. And then he could accept his son Helmeppo again, as Helmeppo reaches the same rank as his father through merit. (Currently Helmeppo has the rank below his fathers captain rank)