I was running RotRL and the party is within the Runeforge area. They've already defeated the Hall of Greed and were in the Shimmerveils were they encountered the Succubus's.
They learned about what was need from the journal and that they need to go into the Lust section.
So since they fought the succubus's in the Shimmering Veil they knew that they used Suggestion, Charm Monster, and Dominate, Vampiric Touch.
So they wizard sent wizard eye into the area of Lust and got a layoff of the area and what lay ahead.
They then cast the following on everyone; Invisibility, Bless, Blessing of Fervor, Protection from Evil, and then silence.
They then cast Haste. Now for Blessing of Fervor it states it does not stack with Haste.
But they were stating they were using the +2 AC, and dodge from Blessing, and the extra attack from Haste, which I said they couldn’t, but they argued they were not getting extra attacks.
Next, since they were invisible they walked right into the main tent were Delvahine’s camber was and since they were invisible got sneak attack.
I tried my best to see what she had to spot them, but when you are invisible and silent not much to do.
Then the one player argued because I had her and her minions attack, but did not try to use Suggestion, or Charm or anything since I knew it would not work.
The problem is these creatures AC’s are 23, and 29. There attacks do 1d3 + 4, 1d4 + 3 etc. and they barely do any damage to anyone.
The barbarian hits and is doing minimum 60-70 damage for one attack.
The Ranger hits and is doing minimum 40-50 damage.
Flying is not an option as the Ranger shots them down, and they give the Barbaian flying. So they can’t get away.
The enemies are very restricted on their options and it just seems the party just walks over all encounters.
How can I make these encounters more challenging without making it like I’m trying to screw over the party?
They then cast Haste. Now for Blessing of Fervor it states it does not stack with Haste.
But they were stating they were using the +2 AC, and dodge from Blessing, and the extra attack from Haste, which I said they couldn’t, but they argued they were not getting extra attacks.
I'm with your players on this. I think, the wording of Blessing is just bad and by choosing +2 to AC and Dodge they get extra attack.
I tried my best to see what she had to spot them, but when you are invisible and silent not much to do.
Well, if pfsrd is to be believed, you can sense an active invisible creature in range of 30 ft with 20 DC perception check. It's not much, but can give motivation to monsters for buffing themselves and be ready for something.
The problem is these creatures AC’s are 23, and 29. There attacks do 1d3 + 4, 1d4 + 3 etc. and they barely do any damage to anyone.
True, but Delhvaine under haste, with inspire courage, arcane strike and TWF can make 7 attacks with minimum damage of 8-9 plus bleed that stacks from whip. And those attacks go with reasonable bonus on hit. If she teleports away, and she must do it if surprised, Delvhaine should use all available time to buff herself.
How can I make these encounters more challenging without making it like I’m trying to screw over the party?
I just used confusion spell. Eagle's splendor gave +2 DC on save rolls from her spells, which bumped confusion to 28 or 30 DC will. And it's not blocked by protection from evil. My party almost killed each other today because of this.
Other advice - don't go easy on them. 12-13 levels means PCs must be prepared to die. Change feats and spells, maximize hitpoints, try to stall them giving time for enemies to buff themselves and attack with all available force on hand at once.
There was a FAQ that recently clarified how Blessing of Fervor and Haste stack. If they choose the AC bonus from BoF they don't get the extra attack from Haste on that turn. However, they can choose one of the other effects of BoF that doesn't overlap with anything granted by Haste.
Similarly, blessing of fervor does not stack with haste, which means that the increased speed, extra attack, and attack roll/AC/Reflex save bonuses wouldn't stack between the two spells, but if you had both spells active, you could still get those three benefits from haste while choosing to stand up as a swift action or apply metamagic to a low-level spell.
But hey, at least you don't have a Paladin with stunning critical. He hit Delvahine on the first round, she failed her save and became stunned. The party cleric stunned her again, sending her to stagger. She was stun-locked for the rest of the fight.