"Oh. In that case you might want to make solving mortality your second priority after conquering Fairyland. Priority order suggested on the assumption that the total difficulty of both tasks will increase if you do it the other way around, which I think is plausible. An unconquered Fairyland would make a poor place to put newly ex-mortals, I imagine, and if everyone stopped being able to die the overcrowding issue would get very pressing very quickly in a way I'm not sure space colonization could solve; on the other side of the equation, while it's possible that solving mortality would put you in a better position to conquer Fairyland, it seems likelier to me that it would provide lots of opportunities for obstacles to arise while you're busy. Such as someone from this world figuring out that Fairyland exists and trying to conquer it first, or someone from Fairyland noticing that you're over here amassing power and deciding to do something about you before you become a substantial threat."