As a matter of fact, Timid can be pretty usable. With a base 100 speed, it can out speed lots of Pokemon and even other Palkia who run other natures like Modest. Here is a recommended set for your Palkia:
[email protected] Orb
EVs: 252 Speed, 252 Special Attack, 4 HP
- Aura Sphere (Good coverage against types such as Ice, Steel and Rock)
- Dragon Pulse (STAB, a lot safer to use than Spacial Rend)
- Hyper Voice/Surf (STAB or normal coverage)
- Dragon Tail/Earth Power (For scouting or further coverage)
Other than hidden power, Palkia doesn't have much against its Fairy weakness. Just keep it away from Fairies, and you'll be good. Hope I helped!