Three things set a Pokémon's baseline: Gender, nature and the ball. Nature shapes the build directly — each one raises a stat by 10% and lowers another by 10%. Five natures raise and lower the same stat, so they change nothing.
The role decides the nature: A Tank takes +Defense or +Sp. Defense, a DPS takes +Attack or +Sp. Attack.
About +Speed: a slow Pokémon can still consider it. But with more and more moves that raise speed — Tailwind, Rock Polish, Trailblaze, Flame Charge — a +Speed nature is worth much less than it used to be.
Look at the stats, the ability and the movepool together to decide which nature fits.
Its highest attacking stat is Sp. Attack, and most of the moves it learns are special.
The stage boosts it gets are special too: Nasty Plot, Calm Mind. So +Sp. Attack is the first choice.
Speed 2.4 is above average, and most damaging moves cut their cooldown by 1s — don't take −Speed.
It will never touch the other attacking stat, so −Attack costs nothing.
Both attacking stats are equal, so lowering either one is a risk later.
When new TMs arrive or the default moveset changes, a mixed Swords Dance + Nasty Plot build becomes hard to reach.
Lower a defensive stat instead of locking the build into one direction.
Sometimes +Attack is right even when Attack is lower than Sp. Attack.
Sceptile's movepool is stronger on the physical side — every +2 stage move matters.
So take +Attack and do not take −Sp. Attack for now.
If things change later, the build can still move back to Sp. Attack.
1.Decide the role first (Tank / DPS), then the boosted stat.
2.The lowered stat should be one the Pokémon will never use.
3.When both attacking stats are equal, don't lock the build into one side.
4.The movepool can overrule the base stats.