Hmmm... ok, I will only post reasons on a few of them... ok?

Twin Tania

Golem-Hey, I like him! Help you in battle... and you have to help him as well. Is he really a boss? Ah, well... whatever.

Grand mummy- Didn't he drop that cool curse ring? Anyway... he's a mummy!

Alte Roit- Much stronger.

Carbuncle- For once this summon doesn't look cute. But it's still usefull at times + harder battle in my opinion.

Azulmagia- Cool blue mage boss.

Halycanos-Seriously, he's the FROG PRINCE!!!!

Siren

Tyrasaurus- Undead Dinosaur!!!!!

Catastrophe

Minitaurus

JuraAvis

Garula-He's a really nice baby, so please... don't be mean to him.

Archeovis

Enkidoh- Gilgameshs partner.

Mellusion

Iron claw

Ifrit

Odin

Byurobolos-This boss can be pretty hard sometimes.

Gilgame- ALL THE WAY!!!!! GO, GO, GO!!!!

X-deth-Soul- Reminds me of Golbez from FFIV

Adamantaim

Dragon grass

Kimabrain

Red dragon

Invisiable

Pantera

Levithan- Cool... but it's sad that you never could face that monster who was swallowed.

Earth Crystal

Atomos- The swallowing thing was fun.

Omniscient