My own special modification

Added 15% chance to fail. Also added so if the event has been triggered even once this round, it will no longer be able to be played again, even event manager panel can't start it again without somehow changing the fired variable to false.

Of course event managers can still trigger individual fish events.

code/modules/events/spacefish_migration.dm

@@ -15,8 +15,16 @@
 										list(/mob/living/simple_mob/animal/space/ray,					1,	1),
 										list(/mob/living/simple_mob/animal/space/shark/event,			1,	1)
 										)
+	var/fired = FALSE //CHOMP Add
 
 /datum/event/spacefish_migration/setup()
+//CHOMP Add start
+	if(prob(15) || fired = TRUE)
+		log_debug("Random spacefish migration failed successfully.")
+		kill()
+		return
+	fired = TRUE
+//CHOMP Add end
 	announceWhen = rand(30, 60) // 1 to 2 minutes
 	endWhen += severity * 25
 	var/list/fish_config = pick(possible_fish_types)