Since we now have an Elite 4, a few things have changed from the old level 100 gyms, this will help you reach the Elite 4.
To have the ability to challenge the Elite 4 you first must have completed all 8 npc gyms.
The Gym Rules: https://www.pixelmoncraft.com/gym-rules
The Gyms:
Rock Gym, level 20, /warp rockgym
Water Gym, level 30, /warp watergym
Electric Gym level 40, /warp electricgym
Grass Gym level 50, /warp grassgym
Poison Gym level 60, /warp poisongym
Psychic Gym level 70, /warp psychicgym
Fire Gym level 80, /warp firegym
Ground Gym level 90, /warp groundgym
Once you have beaten all 8 gyms you can now challenge the Elite 4. The rules are the same as the gyms but you must use the same team for all 4 of the elite 4, you can battle them in any order and there is no level cap.
The Elite 4 /warp elite4
Ice/Ground /warp iceelite4
Fighting/Poison /warp fightingelite4
Ghost/Fairy /warp ghostelite4
Dragon/Steel /warp dragonelite4