Not sure what my favorites and least favorites but ig i can give you my opinions on the bosses
Main bosses
Shura : he sucks. As the fiest boss, his very underwhelming and the only thing is just move constantly
Iris : m1 spam
Ellios : the first actual good boss imo, he actually a good difficulty spike and become quite a roadblock for new players, though i think its a good thing as this shows that the game is not just a easy walk
Argos : AOE spam is a concept but annoying to say the least, though could be a good way to learn how to block
Carina : she get in the way when i just want to pass by, quite a meh experience im my opinion as she just teleports around and beeing annoying
Calvus : i really like this boss, not a pushover and very impressive, tought player to not only be defensive (that one 500! Attack) and on the agresive, pretty good fight overall and the teleports is not too much to the point of annoying, the attacks are well telegraphed and all attacks have its way to be countered
Maria : shes very cool but can be cheese by not going in the ship on second phase, and honestly immunity (while doing the tentacle attack) is not a good thing, the immunity kinda makes the fight disconnect with the flow as you cant fight her and the tentacle can just be ignored as its not targetting you and only attack certain spot
Side
Cerynx : same issue with argos tbh, just block and retaliate
Minibosses
Kai : only having 2 moves is boring, the only thing he have to his name is his high damage
Merlot : to be honest he is alot better than kai having acess to more moves but still, its just like fighting regular people in the end
Alpha : sorry, whooo?
Amelia : now this boss id actually fun to fight againts like yeah this girl is very scary to fight and having lost magic actually makes up for it, though its annoying that she cant get damaged cause “ouh a simple brick is blocking” is not fun
Kalliste : nothing much to say other than he will be terrifying if theres no literal ocean behind him other than that he just pretty generic with nothing special unlike amelia with ult art surge
Evader : his very cool as to even fight him you need to find him somewhere in the sea, the only one where naval combat is actually used and its very nice to have a change of arena beeing in the boat in middle of an ocean rather, and he having his own weapon ability makes up for it
Valerii : tbh beeing the boss on the last wave of the fortress (which imo the fortress too too long and veeery laggy specially on alot of players) is cool and all but he just undherwhelming in my opinion as he feels like "just a high level mage”
Soo overall my favorite boss would be calvus due his fight is quite telegraphed, meanwhile my least favorite one would be maria due to long immunity