Victini

Legend has it that using the Mythical Pokemon Victini will always lead to a sure victory. Sadly, this is not the case in Go. With mediocre attack and a lack of a Fire Type fast move, it's largely pigeon holed into being a Psychic Type attacker, where it has to compete with titans such as Psystrike Mewtwo. It does have V-Create, its absolutely phenomenal Fire Type signature attack, but a lack of fast move synergy and stats just a bit too low to shine hurt Victini's viability badly.

Best PvE Offensive Moveset

• Confusion pairs with Psychic to give Victini its single most powerful and viable moveset
• V-Create is outstanding, but it lacks synergy with Victini's fast moves most of the time
• Overheat is a good move, but it's outclassed by V-Create
• Focus Blast is the worst Charged Move option.
• Quick Attack is basically useless.

Confusion takes advantage of STAB to deal considerable damage. Quick Attack features slightly higher energy generation, but lacks damage output and can't be Super Effective vs anything. 

Psychic offers consistent STAB damage, and ties for the least amount of energy needed among Victini's charge moves. V-create is an incredibly powerful and efficient move, and allows consistent damage output without the ATK debuff that hinders Overheat. However the DEF self-debuff also makes it risky to use. Focus Blast avoids the issue of a self-debuff altogether, but 75 energy is a lot to ask for.