Tromell, Seymours Butler Tromell, Seymour's Butler is an interesting +1/+1 counter card, being able to add counters and proliferate them
Climbers Kicking off with a card from the (at the time of writing) current set, Avatar: The Last Airbender, Badgermole Cub was always destined for big things
Plus theres lots of good tempo/control cards in merfolk builds that can help you disrupt the game until you can start to overwhelm
It's got nostalgia going for it too and would be an awesome addition to the format
Despite having quite a few powerful and historically relevant cards, the Limited format isn't considered 'bomby'
Morph was created by the rules team as they were figuring out how to make two Alpha cards, Onslaught and felt the mechanic played nicely with the typal theme