If you had temporarily gained control of a creature, it won't return to its previous controller
The main disadvantage that Oswald Fiddlebender has is that he needs to stick around so he can tap to activate his ability, but you can rapidly chain things together to set up a combo or try to lock things down
The most important thing Rule 0 on non-cEDH games is to talk with your playgroup before the game starts about how to make the game fun
Final Thoughts These are just my picks for the most outrageous or potent activated abilities in Magic
In fact, a good planeswalker can be worth more than the entire cost of a drop, with the best of the bunch (Teferi, Time Raveler, Jace, Wielder of Mysteries, and Liliana, Dreadhorde General) selling for $60100, while even the cheapest are in the $5 range