The "fatal" damage filter triggers when the entity receives fatal damage, whether that be from a player, or a lightning strike, falling into the void, etc. However, it does not trigger when the entity is killed using the /kill command.
- Enter the provided world, with the example behavior pack and resource pack.
- Summon the test entity (test:sample_entity) using either a /summon command or the provided command block.
- Kill it with your hands. Notice how it shrinks.
- Repeat step two, but kill it using /kill @e[type=test:sample_entity]. Notice how it does not shrink.
The damage sensor on this entity sets a component group that sets its scale to 0.2 to demonstrate that the trigger succeeded.