>>31259647HP Rock hits a lot of Grass' weaknesses, but is stopped by Steel. Best coverage.
HP Fire also works well, especially with sun support, but is stopped by Dragon and Fire.
HP Dark generally hits a lot neutrally, so you could consider just breeding for 5 IV.
Alternatively, you could try Sleep Powder + Dream Eater with a Z-Psychninium. I want to try that on my shiny Lilligant with HP Electric, but it's still stuck in gen 6.
