Castform

Castform is notable for changing its typing in the main series to reflect changes in the weather. In Pokemon Go however, its Normal typing variant is basically useless as it can't combine Super Effective and STAB multipliers, and lacks stats to be viable in the meta. Even as a gym defender, Weather Ball alone doesn't justify its use in the meta compared to superior candidates. 

Best PvE Offensive Moveset

• Tackle gets STAB, but can't be Super Effective vs anything.
• Hex has inferior damage, and lacks synergy with Castform's charge moves. 
• Weather Ball can be used frequently as a 3-bar move, and benefits from STAB. 
• Weather Ball Rock isn't appealing without STAB. 
• Hurricane and Energy Ball don't have any use, and they lack STAB. 

Best PvE Defensive Moveset

• Hex has stronger damage on defense, and is largely unresisted. 
• Tackle gets STAB, but can't be Super Effective vs anything.
• Weather Ball is strong on defense as a 3-bar move. 
• Weather Ball Rock is more likely to be resisted by common Fighting-type attackers. 
• Energy Ball is a downgrade, and is very easy to dodge. 
• Hurricane hits Fighting-type attackers, but is slow to access as a 1-bar move. 

Hex is recommended for PvP due to its superior energy generation, letting Castform spam its charge moves sooner. Tackle gets STAB, but can't be Super Effective vs anything, and is more likely to be resisted. 

Weather Ball is the main and only selling point for Castform, with very low energy costs and good Damage Per Energy (DPE) values backed by STAB. The Rock version of Weather Ball is recommended over the Normal variant due the nature of how Normal-type moves can't benefit from a Super Effective multiplier, despite giving up STAB. Energy Ball costs less energy than Hurricane and can hit common Water-types, while the latter offers a niche against Fighting-type counter picks.