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ALRIGHT
I got leader's crest. Here's how I did it.
I got a venonat with compound eyes on front of the party, then a mon with thief.
Walk around the bamboo area of the main map, find a leader bisharp with a group of pawniard surrounding it.
Use thief to steal the item, BUT, thief doesn't actually steal the item for some reason, so if the item is there, catch the bisharp as well.
I got two leader's crests in a row by just approaching the leader bisharp while having compound eyes in the front of the party.