Q: How does Multi-Shaft work? Do you give it to an opponent or use it yourself? Why would you Take 200 Points?
A: The Multi-Shaft is 100% to be used on other players, however, the Take 5 Cards function, which can be used on an opponent to give them cards to keep them in the round if they are trying to go out, can also be used once per round during your own turn (so either usage is valid, like all Take 5 Cards, as stated in the rules) to give yourself cards to help you to possibly set down.
Q: Can a player go "out" with power cards still in their hand? i.e. - if still holding Steal the Joker, Immunity and Reverse and Double Penalty.
A: Yes, the player can go out; they are Power Cards and do not count in this way, because when players have 0-1 regular cards (and/or FaceEaters) remaining they are out. For example, if you have a d5, you'd need 7 cards in your hand (non-power, i.e., regular & FEs)to have one too many to go out, as you can discard five plus one, your standard discard, and would still have one non-power card left.