Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
Regarding your Nihilego analysis (which looks very good), how about Poisonium Z to OHKO Tapu Lele reliably and Choice Specs HP Ice which OHKOs Landorus-T and Garchomp as Other Options?