It's moves right now are: Surf, Earthquake, Ice Beam, and Brick Brake.
Because skull bash needs 2 turns to deal damage
Hope this helps
It upgrades your defense by one stage on the first turn, then it attacks, It charges, and you can get more damage with any of your moves in 2 turns then it could, so In my Opinion No, but if you have to get it, get rid of Brick Brake
It is a good move but it does take 2 turns to use. It makes your defense go up by one stage also. So you might want to get it but you will be fine without it also. Either way it would be fine. If you got it I would get rid of brick break.
If you want to find out more about Skull Bash: Click this
Hope I helped!