Leaf Storm is a nice alternative to Sub, a move that gives Sceptile more utility against balanced teams, letting it get past common utility bulky Pokemon such as Clefable and Mew. Leaf Storm also secures many OHKOes against offensive Pokemon, such as Landorus, Mega Manectric, Mega Diancie, Gyrados (after SR), Mega Gyarados (so you can always revenge kill it after a DD), bulky Landorus-T after two SR rounds, and probably many more. And, if you choose to go with Modest, Leaf Storm becomes even more of a nuke, hitting harder than LO Latias's Draco Meteor. Here are some important calcs:
- 252 SpA Sceptile Leaf Storm vs. 252 HP / 0 SpD Clefable: 252-297 (63.9 - 75.3%) -- good chance to 2HKO in combination with Giga Drain, sure 2HKO with Modest
- 252 SpA Sceptile Leaf Storm vs. 252 HP / 0 SpD Mew: 229-271 (56.6 - 67%) -- guaranteed 2HKO in combination with Dragon Pulse and SR
- 252 SpA Sceptile Leaf Storm vs. 0 HP / 0 SpD Gyarados: 229-271 (69.1 - 81.8%) -- 56.3% chance to OHKO after Stealth Rock
- 252 SpA Sceptile Leaf Storm vs. +1 252 HP / 4 SpD Mega Slowbro: 368-434 (93.4 - 110.1%) -- guaranteed OHKO after Stealth Rock
- 252 SpA Sceptile Leaf Storm vs. 0 HP / 0 SpD Gallade: 204-241 (73.6 - 87%) -- guaranteed 2HKO after Stealth Rock
- 252 SpA Sceptile Leaf Storm vs. 0 HP / 0- SpD Landorus: 309-364 (96.8 - 114.1%) -- guaranteed OHKO after Stealth Rock
But as far as coverage goes, Grass + Dragon + Fighting is usually more than enough, though if you really hate Focus Blast's low accuracy, Earthquake + Hidden Power Fire is a nice alternative.