Castform (Sunny)

Sunny Castform is great for brightening your day, but not so great for much else. Access to the efficient move Weather Ball isn't enough to save it from its pitiful stats. 

Best PvE Offensive Moveset

• Ember gets STAB and performs best on offense. 
• Tackle falls behind in performance and cannot be Super Effective against any Pokemon. 
• Weather Ball Fire is considerably better than other options, and can be used frequently as a 3-bar. 
• Fire Blast is a downgrade, though it does benefit from STAB. 
• Solar Beam isn't very useful for Sunny Castform's role as a Fire-type. 

Best PvE Defensive Moveset

• Ember hits harder on defense and also gets STAB. 
• Tackle lacks damage output and can't be Super Effective, but at least it leaves Castform less walled out by Fire-resistant mons.
• Weather Ball Fire as a 3-bar can be used frequently before fainting.
• Fire Blast is very predictable and too slow for defense. 
• Solar Beam also has the same slowness and is too easily dodged. 

Ember offers considerably better energy generation and damage output than Tackle. 

Weather Ball is efficient and strong for its low energy cost, and can be used frequently. Solar Beam demands insane amounts of energy which makes it very difficult to access, but provides valuable coverage.