Talk to the Arena Master to enter the Arena, access Arena Island, check your progress on Arena Island or gain access to the Twisted Nether

Commands

Enter Arena Command

/npc Arena Master: give - Cost 1 Arena ticket -- lasts 8 hours, can buy as many as you have Arena Tickets, time adds

Access Arena Island Commands

/npc Arena Master: access buytickets - Costs 10 Arena tickets - lasts 4 hours, can buy up to 24 hours

/npc Arena Master: access buycredit - Costs $10 Store Credit - lasts 4 hours, can buy up to 24 hours

Access Twisted Nether Command

/npc Arena Master: Nether - Costs 100 Immoral Engulfed Object Frags and 50 Primal Essences