Chandra's Ignition says "Creature.NotDefinedTargeted"

[rpherbig]

Describe the bug
Chandra's Ignition says "Creature.NotDefinedTargeted"

To Reproduce
Steps to reproduce the behavior:

1. An AI player cast Chandra's Ignition, targeting Wayward Swordtooth as the creature they controlled
2. It killed Killian, Decisive Mentor and Depala, Pilot Exemplar

Expected behavior
The message should be clearer.

Screenshots

Desktop (please complete the following information):

• OS: Windows

Additional context
n/a