Head to the dungeon with just one well-equipped Soda Junkie, beat the level 50 boss, and leave.*
If you can't manage it, just keep playing until you get stronger equipment. Deep runs on D4 will provide you with more than enough to get through.
*This may or may not be bugged. Other people report no problems, but I had to go through every level--so just click continue at the forks, rather than risk a warp--and manually exit the dungeon. If I left it until he died, or went through any warps, it didn't pop.
As with the others, this will only pop at the end of the run.