Minecraft wiki entry for JSON_format, associated text:  conditions:
 unique_entity_types: The exact count of types of entities killed.
 unique_entity_types: The acceptable range of count of types of entities killed.
 max: The maximum value.
 min: The minimum value.
 victims: A predicate for any of the killed entities.
All possible conditions for entities[show]
 victims: A list of predicates for any of the killed entities. All of the predicates must be matched, and one killed entity may match only one predicate.
: A predicate for any of the killed entities. May also be a list of predicates that must pass in order for the trigger to activate.
All possible conditions for entities[show]
 player: The player that would get the advancement. May also be a list of predicates that must pass in order for the trigger to activate.
All possible conditions for entities[show]