This is a list of all the optional bosses I have in my guide so far. It is being updated by the day.

1:Piastol 1
2:Barta and Rupee
3:Piastol 2
4:Gunarm and Frocks
5:Ixa'ness Demons: Tara, Pera, and Lira
6:Ship: Obisbo
7:Ship: Alania
9:Roc
10:Piastol 3
11:Ship: Giant Looper
12:Elcian
13:Zivilyn Bane