There's no trigger, just walk to the edge of the map where you see the water tower and from a distance you'll see the Spooky Space Kook standing there near the tower. Nothing happens, it's just a fun little easter egg I added.
sigh, Tunky wasn't even in Strange terror from beyond the stars.
Well, it wouldn't work well if I added both TUNKY and BUNKY into Strange Terror. So I had to decide which one to add and I chose BUNKY.