They create a vital incentive for decks to be less one-dimensional by providing unbeatable efficacy against a specific line of play
Transforming After a double-faced card transforms, it's still the same card, so any Auras, counters, or other effects stay right where they are (unless the double-faced card's characteristics have changed such that an Aura can no longer legally enchant it)
Wizards of the Coast celebrated Magic appearing in the next century with what is widely regarded as the strongest set in Masques block admittedly not a high bar to clear
The second option gives all your permanents indestructible for the turn, letting you dodge a board wipe, letting you come back on the next turn for a win
If a creature that's going to meld dies in response to the meld effect, the meld fizzles
Lottery entry dates will be revealed at a later date