Updated information by PotholedSea40: "Bubble Burster's bubble damage is increased the more damage reduction you have when this should have no effect. Because this player is using Shadow Walker, they gain invincibility when they roll (and the game sees this as 100% damage reduction) which means the Bubble Burster one shots everything."
I was trying out new weapons for a roll build and got to this one:
Map tested was ??? (mooshroom land) apoc +25
It seemed crazy good for having no damage boosting enchantments, until it clicked, these mooshrooms normally have a lot more HP and even a raid captain instantly died.
I can't get this to happen firing the bow normally.
Attached gfycat link for some footage, note the raid captain near the end dying in one hit.
Apologies for the low framerate, recorder used doesn't like the resolution.