(A creature with menace can't be blocked except by two or more creatures.) Midnight Mayhem affects only Gremlins you control at the time it resolves, including the Gremlin tokens it creates
The three main rules are that each player must have a deck of at least 60 cards, each deck can contain only two Ink types (Amber, Amethyst, Emerald, Ruby, Sapphire, and Steel), and each deck can have no more than four copies of a card in it
Note that's not him, just any Goblin
If either target of Domri's second ability is an illegal target when the ability tries to resolve, neither creature will deal or be dealt damage
Its far too soon to say which of these archetypes will continue to post numbers once this naturally experimental post-release period is over, but at the very least cards as powerful and flexible as the Virtues, Gruff Triplets and Lord Skitter are going to find a home in whatevers being played