Little late in this, but finally gave this a try & he's not appearing at all in that area, let alone in that little area where you climb up the ladder & find the treasure box.Do you mean the UFO enemy? You can guarantee spawns of it in the TV station: refresh the room configuration so the Treasure Room is on the left, then go in there, there's a ladder that leads to a tiny dead end room. If you have Riberoma(?) and the other one (more enemies, rare enemies) active, he'll spawn every time you come up the ladder. I got like twelve of the drops in fifteen minutes grinding it out.
Edit: Oh sure, NOW it appears after I complain about it.
Edit 2: Think I'm about to face the final boss and....OMG. WHAT.
YOU TURNED INTO MARTH?!?! AND NOW EVERYONE IS SINGING TO THE FIRE EMBLEM THEME?!?! I NEED TO HEAR THIS AGAIN