Sure, Krathos, +4/-2 seems OP. It seems, but it is? Like pointed before, Steam Machine + SoR is also +4 att per turn, and with no loss of HP. Why is this different? Because SoR is a pseudo-rare? I agree that -2 HP is nothing to an Armaggio, but again, whats the opponent doing? How many ways there are to stop the combo? BB, Lobotomizer, Eternity, Rewind, Congeal, Liquid Shadow, Mutation, to list some. This not considering shields. This not considering healing, quanta denial and other strategies. The combo can be awesome, but can be stopped by many cards, and its slow at its start, so I doubt it will even be near the better rush decks we already have.
I just think there is no reason to have a medium powered card, weaker, slower, less versatile, less oriented to its theme, with no reason. Where are the decks to be so feared? If it changes the metagame like Fractal, instead of just making Gravity a possible option, lets talk about whats OP and nerf. Its what I think.