immune triangle?!

[Blauwe vogel]

I'm doing node avalon and the last pillar it the triangle node is immune, even though we're doing the correct order. Am I missing something?

[Megumin's Husband]

attack it with vexcalibur

[Firesomar]

The mandatory path to finish the mission has no combination involving the triangle. The optional ones for the secret chests + intrinsic upgrades do include the triangle, and you have to use the primary fire of Vexcalibur to destroy them.