Years ago, I ws going to my "A" school for the Marine Corps, and started a D&D group (1ed) with a few of my fellow students. I told them all that they could bring in characters from other games as long as they were:
1) legitimate
2) appropriate
3) not "all powerful"
As "luck" would have it, one of the players came to the game with a very high level Ft/MU/Cl with no stat less than 16, that had an arsenal (including a Holy Avenger, a couple of other swords, magial arrows and a magical cross bow), several potions, and a ring on each hand, and a bag of holding with a few more in it (so he could use whatever was needed for each situation). He also had the Hand of Vecna artifact (that he swore he got legitimately. He had a Ring of wishes that he had used to prevent him from being killed. ("I wished that I could never be killed").
This player absolutely swore that it was all legitimate, and that he had gotten eeverything for real and in game.
I figured... well, I won't use the exact phrase I figured, but you get the idea... As he was higher level than the others, I bet him $20 that I could kill his "un-killable" character.
Five minutes after sitting down at the table, I walked away with $20 and he was being watched by the other players as he rolled a new character. My victory ploy? Simple:
He went through an archway filled with mist (he could not die... what was he worried about?) and ended up in what appeared to be a wizard's workshop. There was a young mage there who yelled at him to leave the room 'NOW!".
The player, in a fit of arrogance, had blindly walked into a time portal and had fireballed hiimself when he was an appentice... BEFORE he got the ring of wishes.
I ALWAYS play it straight with my characters and players, and demand that they do the same for me.