Rerolling is the act of deleting your clone and then killing yourself. Instead of recloning you will be sent back through character generation, giving you another shot at building your character. When you reroll you lose all your current stats, skills and mutations, but keep 25% of your total xp. You also keep any money, apartments, and items you had beforehand. Just make sure to put your stuff somewhere safe so no-one steals it while you are assigning your stats.
Rerolling is very common in Hellmoo, sometimes your build just doesn't turn out the way you want it too, or maybe you want to try something new; rerolling is a fairly quick process and if you know what you're doing it won't take you long at all to grind back your skills.
However even with all that you should always think it over before you decide to actually reroll, it can come as a shock to some previously strong players suddenly thrust down to the ranks of the lowly N-tags.
If you're curious about what other builds are like, you could always experiment with alts, instead of rerolling. The game allows you to have up to 3 characters, so you can experiment with a variety of different builds.
Things to do before Rerolling
When rerolling there are certain journals and items you should get that are exclusive to one character.
• Get all the swords such as the Lotus Nodachi and the Fine Katana.
• Get the Deathsuit.
• Get the exclusive weapons from kill journals, such as the Copper Pipe from Charnold.
• Get the excavation utility helmet and any other items that can raise stats (Such as the Doctor's Mirror).
• Tell people that you're rerolling, or it might come as a shock when they gank you and celebrate over the victory of killing a person with 2000 total EXP.
Or you could just go ahead and reroll, if you don't feel like being a completionist. It doesn't matter too much anyhow.