For Maleficent, attack her head and when she breaths fire, stay away. Use mickey cards if possible. Doing long range combos like Omnislash(highly recommended), Thundaga and Ragnarok work well. If you're using enemy cards, no advice here. My select button is broken so I used normal cards the entire walkthrough and still won(MARLUXIA WAS EASY).

For Ansem, whenever you turn into dark mode, DO NOT use Dark Aura and Dark Break. That stupid demon blocks the attacks easily, so it's just a waste of cards. If you're far, use dark firaga. If you're near, attack. In dark mode, if you keep attacking, Riku's attack stuns the enemy for each second attack he does(like 1, stun, 3, 1, stun, 3). Save up as many Mickey cards as possible just for emergency healing. Again, I do not have advice if you use enemy cards.