Thanos arrives on Titan and has his brief conversation with Dr. Strange. He's then surprised to find that "our will" refers to everyone: Strange has used his Sling Ring to summon Captain America, Black Widow, Bruce Banner, Black Panther, White Wolf, Vision, Scarlet Witch, War Machine, Falcon, Okoye, M'Baku, Thor, Rocket, Groot, Valkyrie, Kraglin, Hawkeye, Ant-Man, the Wasp, and Wong to engage Thanos directly.

Round 1: As described above. All characters are as they were at that point in the movie (except Clint, Scott, and Hope, who are given their standard gear). No Stormbreaker, no Hulk. Thanos has the Power, Space, Reality, and Soul Stones.

Round 2: Strange also used the Time Stone to summon Loki, Gamora, Heimdall, Yondu, and Quicksilver. Unfortunately, he also accidentally brought in the Children of Thanos.

Round 3: Like Round 1, but Bruce can Hulk out, Thor has Stormbreaker, and Thanos starts with all 6 Stones--but it turns out there's a seventh one, the MacGuffin Stone, which he needs before he can do something like The Snap. He needs to fight through the heroes using the individual powers of the other six to get to it (Vision is absent in this round for obvious reasons).

EDIT: There's some discussion in the comments of Strange's "this is the only way" and all that--for the sake of discussion, and because he wouldn't bother with all of this if it were destined to fail, assume this is not one of the 14,000,605.