The identity of the third party arriving at Egghead in One Piece chapter 1105 remains unconfirmed until further information is revealed by Oda in the following chapters. However, there are several potential contenders based on various clues and fan speculation:
1. Straw Hat Grand Fleet: A ship with their flag was spotted near Egghead in chapter 1079, and with Luffy currently facing difficulties on the island, their arrival as reinforcements would be logical.
2. Blackbeard Pirates: Their ship was also seen nearing Egghead, indicating their potential interest in taking advantage of the chaos caused by the Buster Call and Marine presence. Lafitte and Catarina Devon remain unseen within the crew, suggesting a possible infiltration mission.
3. Germa 66: Their connection to Vegapunk and possible knowledge of the island's secrets make them potential visitors, further adding to the already complex dynamics on Egghead.
4. Cross Guild: Though less likely, their unpredictable nature and Shanks' connection to Luffy wouldn't completely rule them out as potential interveners.
5. Revolutionary Army: While Dragon and most commanders are currently in Kamabakka Kingdom, a smaller contingent arriving to support Sabo or provide intel wouldn't be entirely improbable.
6. A Surprise Ally: Oda enjoys introducing unexpected characters, so the third party could be someone entirely new with motivations yet to be revealed.