Attaching Dog Umbra to a creature another player controls that's already attacking or blocking won't remove that creature from combat
Not only does Transmogrify fit great in combo decks that aim to cheat out a large creature quickly, but it also acts as situational removal exiling an opponents creature and replacing it with something (ideally) less threatening
Artists for Turbo Gear include Jack Teagle, Evan Stanley, Mike Burns, Sylvain Sarrailh, Tyler Walpole, Tracy Yardley, and Caleb Meurer
I think the first trigger is almost guaranteed if you build a deck designed to cast multiple spells a turn, and the second trigger is probable, but if you double-spell three turns in a row, were you going to lose anyway
It later also appears in Final Fantasy XIV
I imagine the best the card will be will all be at the hands of Windbrisk Heights