Leaf Blade
Leaf Blade is an attack move exclusive to Sceptile in "Pokemon: Ruby." It is a grass attack that gets a bonus to damage due to Sceptile being a grass Pokemon. There are more powerful grass attacks available, but all of these have significant drawbacks. Leaf Blade is accurate and reliable, provides good damage and has an increased chance to do critical damage. This makes it the best choice for Sceptile's grass attack.
Dragon Claw
Dragon Claw supplants the need for Sceptile having a normal damage attack. It is a basic attack ability with no special characteristics beyond doing dragon damage. This damage type does double damage against dragon-type Pokemon and only steel-type Pokemon resist it. This is not a huge factor since steel Pokemon resist almost every damage type. It serves as an attack option when none of your other, more specialized abilities are going to help. It is unusual for a non-dragon Pokemon to have a dragon attack, so you may get the chance to do an unexpectedly large amount of damage against an opponent that fields a dragon against Sceptile.
Crunch
Crunch is a dark damage attack that has a chance of lowering the special defense attribute of its target. Similar to Dragon Claw, it is very unusual for a grass Pokemon to possess a Dark attack. It is most useful for eliminating psychic Pokemon. Sceptile is one of the few Pokemon that is actually faster than most psychic Pokemon. Sceptile basically eliminates all of the advantages of the psychic Pokemon playing style, which similar to Sceptile involves killing the opponent before he can react, without specifically being an anti-psychic type.
Toxic
Toxic is a poison damage attack that does not do much upfront damage, but does significant damage over time. This type of attack might seem odd for a fast attacker like Sceptile, but it can be very useful. This is an attack to use before transitioning to a different Pokemon. The opponent is going to continue taking damage from Toxic for several rounds, which is going to help out Sceptile's replacement in the long run.