What is the best memory to give Silvaly? Would you be able to change the memory after Type Null evolves? Or is it stuck that way?
There is no clear answer to that question.
The choice of the memory type depends on the team you're using Silvally in, as well as on the role that it's supposed to play on said team.
You can change the memories whenever you want.
I recommend checking out movesets either in the Smogon Strategy Pokedex or in the team showcases that you can find in the different tier sub-forums.
Here are two popular ones for you to try out:
Silvally-Water @ Water Memory
Ability: RKS System
EVs: 252 HP / 120 Def / 136 Spe
IVs: 0 Atk
Bold Nature
- Defog
- Surf
- Thunderbolt
- Parting Shot
Silvally-Steel @ Steel Memory
Ability: RKS System
EVs: 252 HP / 228 SpD / 4 Spe
Calm Nature
IVs: 0 Atk
- Flamethrower
- Defog
- Parting Shot
- Toxic
Ability: RKS System
EVs: 252 HP / 120 Def / 136 Spe
IVs: 0 Atk
Bold Nature
- Defog
- Surf
- Thunderbolt
- Parting Shot
Silvally-Steel @ Steel Memory
Ability: RKS System
EVs: 252 HP / 228 SpD / 4 Spe
Calm Nature
IVs: 0 Atk
- Flamethrower
- Defog
- Parting Shot
- Toxic




