So in a group that I'm playing where the GM tends to rule RAW and RAI in favor of the player and lets his players let out their inner power gamer (we're all gestalt), I saw a player with an interesting build. I wanted to ask the community, specifically GMs, whether or not this is broken and/or bannable in a more traditional setting. It involves 3rd party material, so obviously is not an option in PFS.
So here's the main concept of the build. Catfolk ninja/slayer gestalt (but for our purposes we can ignore the slayer aspect, and, yes, I know you usually can't gestalt two rogue-based classes, but as I said, GM rules to player favor).
The key to this build is the catfolk ninja favored class benefit, which is 3rd party: Add a +1 bonus to attack rolls when attacking on or charging from higher ground.
So if you pick this every level, you've taken a 3/4 BAB character and effectively made them a 1 3/4 BAB as long as they attack from elevation. Plus, said lenient GM has ruled that, since wording doesn't specify melee attacks, it can be used when attacking from range. At level 7, our catfolk ninja/slayer, whose favorite tactic is to climb/levitate to a good shooting position, is shooting off 4-6 arrows a round with a +20 attack mod. Now our GM ups the difficulty accordingly and everyone else is just as cheesy so it works. But would any sane GM allow that 3rd party favored class benefit?
So my question comes in multiple levels:
1) would you ban it outright?
2) would you allow it if it applied only to melee combat?
3) how would you challenge a character with this in their build, other than always throwing them in a low-ceiling cavern all the time?
4) If GMs allow this, I'm curious if there are other repercussions or builds that may become interesting with this. For example, if melee only is stipulated, I'd be tempted to take a 1 level dip into samurai (keeping that nice eastern flavor). Mount elevation would make it much easier to get that bonus consistently.