Because Aegislash doesn't learn a single move through level up in XY (you'll have to spend Heart Scales to teach it any level up moves), it may be important to get every move you want through Doublade first. Note that Heart Scales are easy to farm, however, and won't result in much wasted time. The first guaranteed Dusk Stone is in Laverre City, and at that stage in the game a Doublade's most important moves would generally be:
- Night Slash
- Shadow Sneak
- Slash
- Iron Defense
If you're willing to spend a Heart Scale or four (easily taken from any wild Luvdisc), it's a good idea to evolve Doublade immediately after you get a Dusk Stone. You can quickly reteach Aegislash stronger moves like Iron Head, Sacred Sword, and King's Shield, making it a valuable asset much quicker.
Alternatively, if you're not willing to spend Heart Scales at Dendemille Town (unreasonable, as it's very close to where you usually get your first Dusk Stone), it's better to hold off evolving Doublade until one of two levels:
- Level 45, when it learns Iron Head
- Level 51, when it learns Sacred Sword
Doublade has high enough Attack and Defense to still be a valuable member of any Kalos team (though Aegislash is much better), so you can make it work with no Heart Scales. Picking up an Eviolite in Shalour City (which boosts Doublade's Defense and Special Defense) will help in it not being KOed as often, making the grind more manageable.
In conclusion, the much better option is to just spend some time farming Luvdisc for Heart Scales. This allows you to evolve Doublade immediately and benefit from higher stats with Aegislash, and simply relearn its strongest moves just one town later. If you'd rather not do this, waiting to evolve Doublade until Level 45 or 51 is better so it can learn Iron Head and Sacred Sword, respectively. Either way, here's a recommended moveset for an endgame Aegislash:
Aegislash @ Spell Tag
Ability: Stance Change
- Iron Head
- Shadow Claw / Swords Dance
- Sacred Sword
- King's Shield
Changing TMs between Shadow Claw and Swords Dance is an efficient way to use Aegislash, as TMs are infinitely reusable in Generation VI.
