You can indeed win the game this turn with what you drew from the Treasure Cruise. The Become Immense in your hand will do most of the heavy lifting, and you just have to find the right creature for the +6/+6 bonus. Complicating matters, however, is Steve’s Sultai Flayer: you don’t want to kill the Flayer, as that will put Steve’s life total beyond reach.

1. Declare the start of your combat phase.
2. Assign your Temur Charger (3/1), Riverwheel Aerialists (4/5), and face-down Snowhorn Charger (2/2) to attack.
3. Before Steve declares blockers, tap three islands to add (one used as generic mana), one mountain and a Rugged Highlands to add (both used as generic mana), and two forests to add (one used as generic mana) to your mana pool.
4. Spend to cast Whisk Away on your Temur Charger. Put Temur Charger on top of your library. Riverwheel Aerialists’ prowess ability triggers and it becomes a 5/6 creature.
5. Spend to cast Reality Shift on your face-down Snowhorn Rider. Exile the Snowhorn Rider. You manifest the Temur Charger on top of your library, making it a face-down 2/2 creature. Riverwheel Aerialists’ prowess ability triggers and it becomes a 6/7 creature.
6. Reveal Become Immense from your hand to activate Temur Charger’s morph ability, turning it face-up.
7. Temur Charger’s ability triggers. Choose to give Riverwheel Aerialists trample until end of turn.
8. Spend and exile four cards from your graveyard (Marang River Prowler, Treasure Cruise, Whisk Away, Reality Shift) to cast Become Immense on Riverwheel Aerialists. Riverwheel Aerialists gets +6/+6 and becomes a 12/13 creature. Riverwheel Aerialists’ prowess ability triggers and it becomes a 13/14 creature.
9. Steve may block the Riverwheel Aerialists with Icefeather Aven and Archers of Qarsi at best, in which case your Aerialists will deal 9 trample damage to Steve, defeating him.