Thanos makes a call to the Collector. He has been waiting for the call. Thanos tells him he will trade him something extremely rare for his Infinity Gem. He then pursues the Runner.
The Runner's speed is incredible with the space gem he possesses. He is far to fast for Thanos to defeat. But he does not understand the true scope of the gem he obtains. Thanos uses the time gem to turn the Runner into a feeble old man. He takes his gem and then turns him into an infant.
Thanos meets with the Collector and offers to trade the baby Elder for the gem. Collector accepts, saying that the gem he has is useless. Thanos takes the gem and shows him the true power of the Reality Gem he possessed. Collector wishes for him to take it under the condition he allow the Collector to be unbothered in the future. Thanos agrees. But before he leaves he informs the Collector that what he had done to the Runner was only temporary. Runner returns to his normal state and attacks the Collector.
Thanos has saved the hardest task of all for last, obtaining the final gem from the Grandmaster. The Grandmaster is waiting for him and has a game set up to play for it. He has rigged his gem to teleport to an unknown location and explode if he is harmed or he loses the game. Thanos bets his gems that he will win.
They arrive in Grandmaster's virtual reality. They battle but Thanos is far too experienced and gains the upper hand. But the Grandmaster cheats, or at least he thinks he does. The Thanos he has fought was really a robot made by Thanos with his gems, since he himself cheated as well. He takes the final gem, the mind gem, and leaves Grandmaster locked in his own world.
He returns to Mistress Death and tells her that he is now her equal and should be allowed to sit by her side. She creates a throne for him but will still not speak to him. When Thanos questions this, her minions tell him that he is now superior to her, and she would not dare speak to such a powerful being.
He has miscalculated and returns to ponder in the Infinity Well. Although he is victorious, he considers it a hollow victory.