- How do I handle obscene powergaming?
With laughter, all the way to the "Core-only, thanks" Bank.
That can be a step in the right direction, but you can powergame the Core rules to an obscene level as well.
First off all, everyone powergames to some extent, so the first step is deciding as a group what level of powergaming is acceptable.
It is also important to figure out what IS power in your game. Generally it is a full caster, with a maxed out casting stat, spamming save or suck spells. However, it starts as a raging barbarian and evolves as the levels go up. At your table, other things might be very powerful, such as social skills, mobility, or allies. Figure it out before you start to ban things or change rules. Often GM's will restrict martial characters based on the first few levels of the game, only to see casters blow past them after the mid levels. This is especially true in games where the GM bumps up monster hit points. Martial characters are stuck chipping away at a big pool of hp, while casters just shut down the encounter by targeting the creatures lowest save.
In my group I limit starting stats to 17 after racial adjustments. I have also asked players to generally limit the use of action denial spells and abilities, and I use them rarely as a GM.
So talk to the players, come to a consensus on what level of optimization everyone is comfortable with and the problem should be easier to solve.
But yeah, if it is banned in PFS (or beyond the scope of PFS, like high level play, chances are it is generally agreed to be over-power, or require heavy GM moderation.