Xaldin Stamp

Bosses from Organization XIII that gave me a pain in the neck, but managed to beat thanks to mindfulness:

Larxene
Squeaky McSqueakster (Both battles)
Demyx
Xaldin
Roxas (What? It's true.)

All other Organization XIII bosses in my opinion that seem hard to others, but are actually a bit easy:

Marluxia (The first battle was hard, but the final boss forms were a piece of cake)
Zexion (Storywise, I beat him on my second try)
Xigbar (kinda lost count there, but I beat him in less than 3 tries. Secret is to attack him, even when he is upside-down, and the Warp snipe technique is effective as well.)
Luxord (USE THE CAMERA STICK WHEN HE'S BEHIND THE CARDS! It's your best friend. Also, I beat him in One try.)
Xemnas (three times a charm they say.)

I also have an emergency cure button in case I run low on health.