I suddenly came across this glitch in Bulbapedia. Apparently you can teach any Pokemon with Mimic any move you'd like it to have.
So I wanted to see if this is true, and decided to bring my Rayquaza from Emerald with Mimic (I cloned it so a copy stays behind) and I tried to teach it a few moves. I managed to teach it Roar of Time, Aeroblast and Shadow Force. (No 3rd party devices were used, just my DSi and Pokemon Platinum version).
I know these Pokemon wouldn't be legal in Wi-Fi or tournaments, but they're legit Pokemon, I mean a Rayquaza with Roar of Time :D.
Since you can only teach Mimic ONCE in the GBA games, you could simply use Pokemon that learn Mimic naturally like Chatot or Sudowoodo. Wouldn't it be cool to have a Pidgey with Draco Meteor? lol
The video itself is just to show people it's possible (No I didn't want to do it on a ROM, since people will criticize). This is the only camera I have to record any sort of video so can't do much there, and it sucks at recording audio.
I wrote in the descriptions the steps to do this, they're way easier to follow than the Darkrai/Shaymin Void Glitch for example.