Thanos runs a gauntlet with beings he would not be able to compete with head on without prep. But luckily for him he gets 2 days(after stage 12 he gets 5 days) of prep for each fight. Though he may not use the prep time he gets for a specific opponent for another person. Though Thanos will gain the powers of the opponent he defeats each round. Also ff he manages to obtain a certain powerful item such as the IG then he may keep that certain item throughout the whole gauntlet. Thanos gets 5 hours of rest after each fight but he may not use the time for prep.
Gauntlet:
1- Depowered Tyrant
2- Chthon
3- Classic Trigon the Terrible
4- The Vishanti(outside of realm)
5- Shuma Gorath(outside of realm)
6- Galactus(no UN)
7- Death
8- Eternity
9- Eternity, Death, and Galactus(no UN) at the same time
10- Parallax(Zero Hour)
11- Ion(classic)
12- The Anti-Monitor(CoIE)
Now Thanos has 5 days of prep
13- Galactus shoots the UN only once at him
14- Mr.Mxy
15- The Ultimator
Galactus is no prob, he's already done this on panel with a similar level of prep (dropped a planet or moon on big G). For Death, Thanos could just prep up some ultimate weapon that destroys a few billion people and "woo" his way past Death. But to get to that level of the gauntlet I don't know. I can't figure out how he could get past the vishanti. I could see him talking/bargaining his way past Agamotto like Strange has in the past but that doesn't get him past the other vishanti.
tyrant is easy, all he has to do is amp the orb he stole (if he hasn't already) with any of his other insanely powerful technologies to tip the scale against him.
i won't even bother talking about the characters after him since a fight with them is hard to imagine.
Anyways, he uses his time to steal the UN and clears this the first part of the gauntlet.
Pulls the trigger and kills Anti-Monitor or resets all of space/time to before Anti-Monitor consumed the multiverse. Then kills him with a second shot. Galactus can't fire the UN because Thanos already stole it from him. Thanos fires at Galactus, sadly Galan does not survive.
He tricks Mxy into granting him all his powers and then kills him. Then he uses Mxy's powers to beat Ultimator the same way Mxy did (with Mxy's powers he'll see into the past of how Ultimator was beaten by Mxy).