Mushroom 1 - Every time he reverses himself, wait approximately 1 second or so before reversing yourself. There is a slight delay between the end of his reverse animation and the the beginning of his attack one and you'll find it's like time slowing down if you don't mash the reverse button normally. Then just hit reverse once and he'll be confused straight away.
Bit hard to describe but instead of reversing instantly when he does, let him finish his reverse animation, hold a split second and then reverse. Worked every time for me.
Mushroom 8 - Took me like 2 hours of no dice yesterday. Did it first time just now though. What I did was use Master Form, two keyblades with reach, remove all MP abilities and equip the Berserk ability and the Horizontal Slash ability. Then, use Curaga to waste your MP bar, throw him in the air, do a combo, do 4 horizontal slashes, another combo, some more horizontal slashes and continue. I found that by alternating these rather than just one permanent combo blitz, his tendency to fling himself too far away from you was lowered dramatically and I got 94 hits.
This is purely based on luck though.