Just win 15 Multiplayer Ranked matches to get this achievement.
This achievement is pretty hard to get because there are almost no players online. So you have to find a partner to get this one.
The fastest method:
- Start a new lobby (must be ranked)
- The other person is going to search
- You will met eachother within a couple of seconds
- Start the match (Press X then START)
- Kill your self by placing blocks horizontal
- Repeat this 30 times
You should get the achievement in about 15/20 minutes