According to tibia wiki and tibia fandom, to face it you need to have the 2nd rank of citizen in Rathleton and a vote in your quest log. Talk hi - fight - yes to the NPC who is at the location marked to be teleported and use the lever to go to the boss.
My doubt is about how many players can enter to face the boss, since you don't have the lever with player limitations to fill.
Lisa - Tibia Wiki
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