bees
also in the same map as the one youre bursting at with frogs,
it is in the west side just below the farm

you need to position your team where 2 sets of bees spawn, they spawn for less than 10 seconds after you finish a battle.
1st set is 2 (none) element bees
2nd set is 2 (wind) element bees

so after finishing the 1st battle, the second set of bees will approach you to start another battle.

note that you must not be laggy so all your chars can recover SP before going to next fight.