I literally don’t have the resources to test this, does ‘prevent 100% of that classes base damage’ mean it blocks all attack and spell damage from that class? has someone tried this with success?
It blocks damage from spells and attacks, like it says. It doesn’t block other damage sources (like which are triggered from some traits like the Brim Smith’s) so you can still die from these creatures.
If you’re worried about dying from the non-sources, add a phase knight to your team.