for good approach tactics look at the metaknight's approach thread after you have made contact, then the comboing begins, one that i really like and that looks pretty cool, is to use Ftilt combo to pop opponent up, then chase with the rising Uair combo til you are out of jumps/the opponent is above the screenand then switch to UpB to kill/glide chase and attack again. another good tactic is to run in, grab, Dthrow, Dthrow,Utilt/Dsmash and then chase. also you will want to use metaknights aerials as much as possible, who doesn't, but make sure you don't get to predictable, maintain proper spacing, and don't neglect your B moves, lots of mk players i have played so far spam aerials, but forget about the B moves, i recommend B/UpB highly, DownB, slightly, and a rare FwdB. and if you are knocked off the stage, but don't get KO, you should ALWAYS make it back. mk has the best recovery in the game and can get back from anywhere on the stage if done properly. make sure to utilize all 5 jumps, his 5th jump glide, his UpB to glide, his rising tornado and his FwdB Drill move. hope this helps! good luck and happy practicing.