A very easy achievement. Put it on beginner,one round (thanks ninja) and choose Noob Saibot. He is just way too good and a very easy character to use. All you have to do is ( down,forward a ) which sends your shadow running and will tackle your opponent and then press ( down, up ) and you will teleport to your opponent and slam him into the ground. I pretty much just used those two combined with my x-ray and i won every match with ease. You can even throw in ( down, right, x ) and shoot your little electrical ball at your enemy just to mix things up a bit. All you have to remember is to never block an attack. Feel free to use RT (block) for moves/fatalities but dont actually block an attack.
if you do die just hit continue and try again.
you will also unlock another achievement for beating the ladder if you havent done that already.
i cannot confirm it but i assume you can also get the tag team one as well if you never block.
Tried it in tag team but didn't unlock for me.- BadTriangle
For anyone who may be wondering, I played through and used block to do some stage fatalities and I still got the achievement. I know that's a minor detail, but still potentially useful! - Cyprus Church