Timetwister is usually considered part of the classic power 9, but in my opinion it isn't on the same level as those mentioned in the first catagory (don't get me wrong it is a very powerful card but if someone had a cube with only it in from the classic power 9 and labeled it unpowered I would not complain)
Mind Twist is an evil card - but not bad enough to consider "power" - especially if the fast mana is removed. Personally I've lost more games to Recurring Nightmare and Bitterblossom than Mind Twist so in my mind this should not be considered a power card
Edit: Balance is another I'd consder up there that I missed. Again not nearly as bad when you remove the fast artifact mana from a cube though so i'd put in in the same catagory as Timetwister
Other potential considerations:
And if people call all fast mana over powered they should not have:
Timetwister is usually considered part of the classic power 9, but in my opinion it isn't on the same level as those mentioned in the first catagory (don't get me wrong it is a very powerful card but if someone had a cube with only it in from the classic power 9 and labeled it unpowered I would not complain)
Mind Twist is an evil card - but not bad enough to consider "power" - especially if the fast mana is removed. Personally I've lost more games to Recurring Nightmare and Bitterblossom than Mind Twist so in my mind this should not be considered a power card
Edit: Balance is another I'd consder up there that I missed. Again not nearly as bad when you remove the fast artifact mana from a cube though so i'd put in in the same catagory as Timetwister