Expedition: general discussions.

The grandma uses Psychic protection.
The mouse uses "Madness Spray" on the grandma. The grandma goes mad and kills herself with a kitchen knife.
Grandma: Eh, but I have Psychic protection!
DM: Well, it's supposed to protect against magic, but this is a special gas, and the mouse sprayed it at you.
Meanwhile, the creature is nimbly climbing up the table leg onto the table.
Grandpa: I drink a potion of invulnerability.
DM:
Grandpa drinks the potion of invulnerability, gaining invulnerability until the end of the battle.
The mouse uses "Absolute Freeze," and Grandpa is frozen until the end of the battle. He helplessly watches as the terrible beast kills his friends and then waits for the battle to end so it can get to him.
Grandma: I cast a fire shield on myself.
DM:
The grandma uses a fire shield.
The mouse uses "Death Claw." The grandma takes 10000 damage [-9700/300]. The mouse takes 800 damage (affinity to fire, damage is converted into healing) [20800/20000]
Phantom: I don't believe in this creature.
DM: It's real...
The Phantom tries not to believe in the mouse (no effect).
The mouse uses "Death Claw." The Phantom takes 10000 - 10% = 9000 damage [-8500/500]