There are several base properties, some are required, everything else has a default value. Note: Mob Event Spawners have a base property that assign them to a mob event so they do not need to be listed in the mob event json at all.
The unique name of the mob event. Required.
The non-unique title of the mob event, can be the same as other mob events names or titles, this is used for the event's printed name, textures and sounds. Optional.
Whether this event is active or not, this bypasses all checks and triggers, etc. Use this to disable default events or to turn off custom events without deleting them. Default true.
The channel that this event should use. Can be: world (affects all players in the world), boss (for boss events) or player (the event is unique to the player, for area events). Required.
How long (in ticks) this mob event will be in the spawning phase for. After this the event is considered over but spawned mobs may linger. Default 1200 (60 seconds).
Determines how many Conditions must be met. If 0 or less all are required. Default 0.
If set to true, when this event starts it will stop any active event on the world channel. Events on the world channel normally wont start is another world event is active but this will override that as well. Default false.
The minimum amount of levels to give a mob spawned by this event. Default 0.
The maximum amount of levels to give a mob spawned by this event. Default 9.
array[Spawn Condition] conditions
A list of all Spawn Conditions (same as the ones used by Spawners) which determine if the Triggers should be active or not. Default empty (Event will always be allowed).
array[Mob Event Trigger] triggers
A list of all Mob Event Triggers (different to the ones used by Spawners) which listen to events and ticks and attempt to start an event, if conditions are met. Default empty (The event will never fire unless done by command).
array[Mob Event Effect] effects
A list of all Mob Event Effects which perform various actions during an event. Default empty (No special actions).