Virtually everyone in pro wrestling has made use of what is the most iconic improbable weapon in the industry (heck, maybe in all pop culture): the steel folding chair. That it's synonymous with the profession should not detract from how odd it is to use one in the first place.
Practically every signature weapon used by any wrestler. The most iconic example in the business may be the original Sheik, who would carve his opponent's flesh with a sharpened pencil or launch fireballs at them. The second most iconic may be the dreaded fork of Abdullah the Butcher.
Finlay is known for using the ring apron as an impromptu net to trap opponents.
ECW's "The Innovator of Violence" Tommy Dreamer earned his nickname from his ability to make seemingly ANYTHING into a weapon (regularly leading to announcer Joey Styles saying, "The Innovator of Violence strikes again") , ranging from piledriving Raven on a cream pie to applying a cheese grater to Brian Lee's groin (which prompted Joey to say, "I'm not calling that.").
Averted by Triple H and his sledgehammer, which is not really an improbable weapon, except, of course, because of safety concerns, he can only bludgeon other wrestlers with the head, rather than swinging it at them.
William Regal and anyone else who made use of brass knuckles also averts this trope.
In Progress Wrestling Paul Robinson has used credit cards (in an attempt to give Will Ospreay a Glasgow Grin) and a bible (to hit Pastor William Eaver with)
In Dragon Gate, the favored foreign object, used by stablemates at ringside to interfere during a match, is a large, brightly-colored plastic box. The blue box was a trademark of the heel stable M2K, and since then color-scheme-appropriate boxes have been used by the heel stables — Mad Blankey's was yellow, Aagan Issou and Verserk used red, etc. Jimmy Kanda, a founding member of M2K, often uses the original blue box despite being a face.