ToME: the Tales of Maj'Eyal

In forbidden crypt, the one with the rats, shadows took no damage, tool tip says -100 light resist but light damage was always zero. I think it also happened in heart of gloom. Nightmare difficulty if it matters. Could not damage with physical either.


And as mentioned elsewhere summons are very overpowered everywhere on nightmare difficulty

That's probably fade, the shadow's talent that lets it evade damage. Check their talents.