New DM here. I have a player running an Oath of Conquest paladin. He makes a pretty convincing argument that as he increases his armor class, he becomes harder to hit, and Armor of Agathys triggers less often; but increased armor often translates into increased weight.
Wouldn't the increase in weight make him easier to hit (slower movement, less agile), or at least a melee weapon should be able to hit his armor easier (whether or not it's a hit on him is entirely different).
The spell says it triggers on a hit; but it also says it encases the character and their gear… does Armor of Agathys trigger when the attack roll that tries to hit the player does not clear the armor class?
Best Answer
Armour of Agathys only triggers on mechanical hits, not narrative hits.
Here, "hit" is a game term that means the attack roll against you beats your AC. This is regardless of whether you describe a miss as bouncing off armour (narratively a hit) or being dodged (narratively not a hit).
Previous editions did attempt to distinguish between these types of hits and misses, for more details please see Is your character's ability to avoid attacks based solely on AC?
Also bear in mind, that spells only do what they say they do. Armour of Agathys doesn't make you mechanically heavier or easier to hit. But you're welcome to narrate the outcome of effects as you please.