I like the card idea. It has a similar effect to pharaoh in which the cards that it creates become stronger when there are more of them. I dont necessarily think you need to make a new second card, unless you are following the ambush series. Gravity already has a low-mid range attacker that is perfect for summoning, which is Gravitation Mercenary. Giving gravity 2 more creatures is in my opinion unnecessary considering it already has Graviton Mercenary that fits the role of the soldier. It would also make Graviton Mercenary more played, since very few decks that I know of use it. I think that the cost of the Captain is a little high, but you could change that by either making the cost a little lower or adding some sort of passive skill that benefits other gravity cards slightly since it is a Graviton Captain and it "leads the troops" so to speak. This ability could be something as simple as gravity creatures getting a small attack/health bonus, or something such as one gravity creature attacks twice with the second attack being half of its regular attack rounded up. This card could open up some good gravity/time duos with scarabs, with both elements using quanta from the other element. Overall, this is a very good and clever card idea.
