Grumpig

Grumpig is a dex filler from the Gen 3 Hoenn region. The lack of stats and suboptimal movesets puts Grumpig significantly behind current Psychic-type meta Pokemon, and it's not exactly impressive for gym defense either. 

Best PvE Offensive Moveset

• Extrasensory benefits from STAB and is superior to Charge Beam.
• Psychic outperforms Mirror Coat on offense by a considerable amount. 
• Shadow Ball lacks STAB and is better for other Pokemon. 

Best PvE Defensive Moveset

• Extrasensory hits harder on defense, but is walled by Dark-type attackers.
• Charge Beam is inferior stat-wise, but is less likely to be resisted. 
• Shadow Ball is easy to dodge, but provides coverage against the weakness to Ghost-type attackers.
• Psychic is better than Mirror Coat in every way, and is also the hardest to dodge. 

Extrasensory is generally favored for its superior STAB damage output, though Charge Beam has a slight edge in energy generation. 

All of Grumpig's charge moves cost the same amount of energy, which means Grumpig doesn't have to bait shields, however they are all moderately expensive. Shadow Ball is quite powerful and provides relatively neutral Ghost-type coverage (including against Grumpig's weakness to Ghost-types). Psychic outperforms Mirror Shot and makes the latter irrelevant.