I feel your pain. If it's any comfort, my furry demon is actually well-behaved when I'm gone. But then, much of his mayhem is done in the name of getting my attention. If a tree falls in the forest and the human isn't there to squawk about it, what good is it to him?

Be very wary! He has a plan, and it involves world domination!

I have to admit I amused by kitty hijinks, but I recognize they can be frustrating. I suppose I am extra amused because my kitty, Riddler's littermate, doesn't seem to get up to the same hijinks.

In thinking about that, though, something occurred to me that may/may not help you.

I've noticed that Nim (again, Riddler's littermate) has entered that phase of being a young cat after the kitten phase where she has loads of extra energy. In my house, this is mitigated by my extra roomates, who play with her a lot. Two of my roomates are home during the day, so Nim effectively has a potential playmate nearly 24/7. On top of that I play with her fairly regularly when I get home-- a lot of really physical play. I've noticed that in weeks where I haven't gotten to play with her and my roomates are also busy, she runs around like a psycho maniac, kind of like you describe Riddler. Sounds like maybe Riddler got used to having someone at home, much like Nim?

So my more serious question is to ask what sort of physical play Riddler's getting, and/or what toys he has?

Like with a kid in the 4-10 range, maybe Riddler's acting up because he's not getting enough physical activity, or at least that's some of it. (Even being spoiled rotten for attention, Nim still will get into anything dairy that is left out-- including licking all the frosting off a cake).

I have one of those cat toy on a string and stick toys (a kitty fishing pole) which she chases lots until she's tired or I am. Even then, I have a way of setting up the pole so that the cat toy hangs and she still plays with it. Does Riddler have a toy that hangs that he can play with even when the humans in the house are busy or not there? I know Nim is a sucker for anything on a string (though sadly not the laser pointer), and will play with hanging toys either until they break/are torn apart, or until she exhausts herself, so I have found sturdy hanging toys (leather/solid fabrics>feathers/floofy things) to be a good investment. She also has some loose toys to chase around.

Also, our house is a 2 cat house, and I've found that it was important to make a distinction to the cats re: which toys were whose. There were issues when Nim was just playing with Moose's toys (Moose would hide them). So I started taking Moose's toys away from Nim and giving them to Moose, and giving her her own toys to play with. Now Nim plays with her toys and Moose plays with his toys, and both sets are actively being played with. So maybe another issue is that if your cats are 'sharing' toys they mostly end up hidden and stay hidden so the other cat doesn't get them?