Changing stat blocks is fine in principle but the changes being called out here are pretty aggravating. Every Goblin having an AoE attack item or secret special move just gets frustrating. If you don't split your party in prep of every encounter expect to be fire bombed before you even take a move... against a couple of goblins. Or there's the Mud Quasists. As written they have an ability that once a day lets them summon 25% chance of summoning 1d4 Quasists, so on average about 0.6. In this they have a per turn ability that summons an add. I mean if they had 100% chance of summoning one that would be on average a 50% buff, but one per turn. It's just annoying and drags the encounter. That's before you take into account that they seem to get ranged attacks of opportunity or the terrain makes dealing with the mobs popping in an out of cover cheesing the encounter slow to deal with. It's like playing D&D with a DM that's actively trying to kill the campaign.
