These two go head to head in an all out battle to the finish.
Gladiator is at his peak levels, with the stipulation that he doesn't weaken when he loses confidence.
Thanos is at his natural level if power, meaning no tech/mystical upgrades or weapons. It's just his strength, durability, cosmic power and his intelligence.
Khazan Arena, no prep-time. They meet, then fight with all their power.