So, my DM is being stubborn again. He goes by the rule of 'if it has the same name, the buffs don't stack', so for example if you wear two armors, it doesn't matter, the bigger AC bonus is the one used.
And that's fine and dandy.
But he claims that things like rage, mutagens, enlage person, potions, spells and stuff don't stack with one another, even though rage is a morale bonus, mutagen is alchemical bonus, enlarge person is size bonus, etc.
What's the ruling here?