Typically speaking, a character's backup plan doesn't come into effect until their first plan fails in some way (such as it being destroyed or countered). Since Invocations leave the field after being used, Twisted Souls would only be used if Naara's life drops dangerously close to one, and ONLY if they would want to keep the game going ("Oh come on, I'm not even having fun yet! Oh, I know, I'll use this!")

That being said, I'm not sure I understand why it would force everyone to make new cards, since I thought it was clear that it applied to all instances of damage/healing, including anything the Player does. The generic staple Salve becomes "Deal 1 damage to yourself", and Fireball becomes "Target competitor gains 1 life", and any damage dealt by warriors becomes healing.

It is confusing, but that's kind of the point when up suddenly becomes down and left becomes right.