So basically, as someone who's bested AOTM on critical it isn't that big of a deal. like with basically every boss in this game thunder surge is your best friend. You should have 5 thunder surges and 3 cures in your deck as well as the abilities second chance, once more and leaf bracer. Cure block is also handy as you'll be blocking a lot, so treat yourself to some healing.
Learn his pattern and retaliate. Block, dodge, attack, etc. Like other bosses his defense is extremely high but not as brutal as vanitas' sentiment. The chain/rock attack is basically impossible to avoid so brace yourself the best you can.
Tl;dr wittle him down and throw his shit back at him. Good luck with no heart.