A very powerful melee creature with substantial hitpoints to survive many attacks. They can move as fast as a level 50 player so lower levels should avoid them. This is the only undead which is weak against Death Damage.
Paladins: You should use a blocker or a mage with some mass spells to clear the floor of the arena first, and once that has happened, there is plenty of space to run the gladiators. Because of their high defense, you should use strong weapons, even with high skills.
Knights: They hit very hard so skill levels of 80/80 and at least level 50 and good equipment is recommended. Only high level knights will profit, so try to get a mage to heal you. If you solo, it's usually wiser to fight 2 at a time instead of one, because you will be using exori/exori gran often just to get some damage through their great defense. Exori will hit both gladiators and will yield twice the experience for almost the same amount of mana.
Sorcerers: Should use a Wand of Starstorm or Wand of Voodoo since these are elements they're weakest to for wands, and use Terra Strike. If it's too crowded and there are several gladiators on the floor, use energy wave to clear the groups while running them. If it gets too tough, you can go between the beds on the bottom floor to narrow them to one direct attack at a time. Recommended for levels 60+.
Druids: Should use a Springsprout Rod and Terra Strike. The combination will drop the gladiators quite efficiently. If things get tough with a group of them, use Terra Wave to clean them out fast. Recommended for levels 50+.