I've been making a forretress, can someone tell me if this is good or not? xD

@ Leftovers

Impish - 252 HP 129 Atk 129 Def

Stealth Rock
Spikes
Rapid Spin
Explosion

It's more of a utility pokemon in my team, since I think I would need a spinner. But is it bad to have both stealth rock and spikes on one pokemon?

Also, how do you calculate damage for stealth rock and spikes if someone can tell me. Thanks

Also, special thanks to crunchy, he helped me with this ;D

Stealth Rock - 1 layer max

4x resist - 3.125%
2x resist - 6.25%
normal - 12.5%
2x weak - 25%
4x weak - 50%

Spikes - 3 layer max, hits anything not levitating/flying, and those with iron ball (or if gravity in play)
1 Layer - 6.25%
2 Layers - 12.5%
3 Layers - 25%

I think thats right

If you want Forretress to explode, I'd think you would want another team member to Rapid Spin for you. Should you explode your Forretress while your opponent's Skarmory, Hippowdon, etc. is still alive, they can still put up rocks and spikes.