Encounters

[MrDeimos]

This is almost definitely related to party make-up, and/or enemy tactics.

In terms of Party make-up, what is the party like, both on the character builds but also with the types of players. Character builds are often influenced by how the players play. Are most of your players Power-gamers? If so, you may definitely have to build around that and fight them on a similar level.

This brings us around to enemy tactics. Simply put, when using pathfinder monsters, they often have a tactics section, and you best make plenty of use of it, because they are very good things to follow. If they don't have a tactics section, get inventive. Does your enemy have a way of getting away from players, such as invisibility or movement types they don't have access to? Make copious use of those things. Make sure that they are using all the abilities at their disposal. If they're fighting a dragon, make sure they aren't doing it in an enclosed space otherwise the dragon can't fight smart, stay in the air, and breathe down on them from 60 feet up. As well, make sure they use combat maneuvers such as tripping, grappling, hell, if you're not afraid of breaking their gear, start sundering their items. You'll find that when enemies fight smart the players may have to adapt or die.

As well, numbers are your friends. If they can rip through a CR 15 and A CR 13 at tenth level, start throwing more at them. try it with three CR 15 and two CR 13 creatures. the biggest problem with this system, is that players can wreck the action economy with no problem, when there's only one monster to fight, they better be a wall of hit points and turns, or they're going to die very quickly. there are three-and-a-half solutions to this problem:

1.) The More enemies the better. More enemies that split the party's focus big time, leading to at least longer fights, and possibly more difficult/challenging encounters.

1.5.) As an extension of the more enemies thing, start adding on things that are different monsters technically but are actually extensions of the boss itself; think Baigan's arms in FFIV or Culex's Crystals in Super Mario RPG.

2.) Make bosses function differently. Multiply their hit points and give them additional turns in the initiative, these should likely scale with each other (Multiply their hit points by two, give them two turns per round instead of one). Give them immunities to status effects that aren't on the list (individual spells), let them remove status effects at certain Hit Point Markers. Give them additional Elemental resistances or increase them and damage reduction.

3.) Interesting terrain. Place traps and manipulable elements to the battlefields, give the players and enemies opportunities to manipulate the battle for better or for worse. maybe activating a trap will give an advantage to the boss. maybe it just does damage. maybe it straight-up kill them or knock 'em out, instantly. you can do that at this level. Just don't like, perma-kill them. maybe the big monster and flail around on the ground causing stalactites to fall from the cave roof. falling on top of the players, dealing additional damage. that kind of thing can make a fight challenging but fair. In D&D 5th edition, dragons while in their lair get "lair actions" on initiative 20 that act as them manipulating elements of their lair to throw off or deal damage to the players. Maybe adapt that to make fights more interesting.

Bless you