Only problems I had were the Mario/Squirtle freeze when they do the water attack, clear special brawl mode not working and coop event match 6 not working, and slowdowns.
Solved the problem entirely by :
-Having the Wii on 50Hz
-Turning deflicker off in SSBB
-Going back to the Wii menu and putting it to 60Hz
-Optional : Putting deflicker back on because I get quite a lot of flickering, but you must remember to turn it back off before turning the game off, otherwise you have to restart the procedure
Turned out this solved the slowdowns, the water freezes and the clear brawl not working. As a consequence, coop event 6 works now because it is based on clear transparent characters.
(As an aside, I'd like to know if it's possible to solve these problems on 50Hz, as when not at home I use my adaptec gamebridge to play on my laptop screen and it doesn't support 60Hz...)