I don't think you guys are thinking hard enough about how mewdos would play. With lostgar, you are trying to lostzone pokemon as quickly and as many as possible. The goal involves the quantity and speed of the cards you are lostzoning, as opposed to the quality. Of course, if the gar player had the choice between karp and dos, karp would be the obvious choice. But oftentimes, early game and later on after tomb drops, hurl of darkness is a blind attack. With decks like gdos, it is easy to manipulate the cards in your hand, and the remaining cards of your deck. Even if they don't mean to, I feel like the lostgar player would still end up lostzoning a gdos before any karps in that matchup.
Also, how can you say that it is a problem for the deck deciding how many mews to run? That is a problem for the player that is obviously going to be solved before the tourny. Theoretically, any player could just tech in a psychic energy and 1 mew into a normal gdos deck (the psychic energy would be an interesting play used with ditto, also). With the probable increase in the play of cyrus in gdos, this is just that much more viable. Impersonate cyrus for a collector, psychic, and a turn. Next turn, collector for mew and karps and discard them. Don't say that cursed drop solves this problem, because you need 2 turns to do that. As long as mew stays on the bench, he is basically safe because a seeker is a guaranteed way to waste a turn for lostgar. When mew is attacking, he should 1-shot every gar he sees. It takes 2 turns to build a cursed dropping gar, so you only need to heal every other turn.
