A titan nuke, essentially. Similar to the Seraphim's Mega Nuke That Is So Awesome Noone Can Ever Build It. Here's the Things to keep it within reason: 1) Orbital Structure built by (you guessed it) Orbital fabbers 2) Really good health (10k or so, at least) 3) Constructs either multiple nukes that can be launched simultaneously (not very awesome) or a Mega Nuke that requires two ANukes to take down (much more awesome). Also, the Mega - oh, screw it. UBER Nuke. Why not? Anyway. The Uber Nuke would have a significantly larger AOE than a standard nuke. And a mind-blowing model 4) It can only fire at other planets. (This will be tough to mod, but we'll see) 5) Costwise, it should cost a lot to build but also cost a ton to maintain. Unlike the Seraphim's Yolona Oss, which cost basically nothing to run and would end the game, no matter the situation, within minutes. 30K to build, 30k per nuke would work, I think. (Yeah, it's the same as a regular nuke missile's cost, but shh.) 6) It should NOT (I repeat, NOT) be a copy of the previously mentioned Sera Nuke, balance or otherwise. Pls no. It should be another doomsday option for the orbital layer. Also, it should be represented by the most awesome model you've ever seen. I'll make a mod for it to test out the balance in some games.
