Back in the day enchanters used to go the newbie zones drop an object like a coin or a sword on the ground and then cast minor illusion on themselves and then pick up the object. The chanter upon casting the spell would turn into object they had dropped. They would then wait until the newbies came along and enjoy the reactions when they tried to pick up "object." If they were transformed into a sword they could spin around just before the newbie came too close and many times they would back off in fear. The abilty to do this is no longer in the game.
Another prank that I used to do when Luclin was new was in the tunnel leading to Fungus Grove. There was a lot of traffic along this long tunnel when the expansion was new. There are these objects (not mobs) in the tunnel that look like pink sea urchins with tentacles. They would root lower level players for a few seconds. I would go to a bend in the tunnel where some of these tentacle urchins where and cast minor illusion and I would turn into a HUGE and I mean HUGE version of one these that could spin around waving its tentacles with great menace. Players running back from FG would turn the corner and come face to face with a huge "named" monster. I cannot tell how fun this was. Many turned and ran away and many froze in fear. Then they would all realize what was going on, some quicker than others and they would get a big kick out of it.