K.B.
Since he is doing such serious damage, the first thing I would do is take everything that can be dangerous or seriously destructive (markers, scissors, knives, crazy glue, etc.) and get it out of his reach.
The second thing I would do is choose a system and stick with it! If you've tried all of the things that you listed all since his behavior changed in late April, that's not being consistent. It sounds like in a 6 week period you've tried 3 or 4 different techniques. Nothing is going to work the first time. Or something might work the first time but then he'll test you the second time. A system is only going to work for the long term if the child realizes that it's not going to change and he is stuck with the consequences. You've shown him that if he doesn't do what you want him to do you'll change the "game" and not stick with it.
Good luck,
K.