How to beat Journey Down the Anduin in Round 1

The best solution I've come up with to this challenge is three players, and using a third Sneak Attack. For a single core set, it is relatively trivial to beat it solo in 2 rounds, using the same hero lineup and technique as Passage Through Mirkwood.

3 players, 2 core sets, 1 round:

Deck 1:
Legolas
Gimli
Thalin

Hand:
2x Blade of Gondolin
Horn of Gondor
2x Quick Strike
Blade Mastery

Draw: Veteran Axehand

Deck 2:
Aragorn
Theodred
Gloin

Hand:
3x Sneak Attack
2x Son of Anor
Gandalf

Draw: Steward of Gondor

Deck 3:
Eowyn
Dunhere
Eleanor

Hand:
Unexpected Courage
Stand and Fight
(other cards are irrelevant)

Staging: Reveal Hill Troll, Despair x2.

Planning:
Play Steward of Gondor on Eowyn & exhaust it
Play 2x Blade of Gondolin on Legolas
Play Horn of Gondor on Gimli
Play Unexpected Courage on Legolas (3 Spirit resources left on Eowyn)
Use Sneak Attack to put Gandalf into play, dealing 4 damage to the Hill Troll (5/9 HP remaining)
End of phase, return Gandalf to hand, Gimli gains a resource.

Quest:
Discard Son of Anor, Veteran Axehand, and an irrelevant card to boost Eowyn.
Use Stand and Fight to put Son of Anor into play, engaging the Hill Troll.

Commit Gimli, Thalin, Aragorn, Theoden (resource to Gimli), Gloin, Eowyn, and Dunhere to the quest (16 willpower), along with the Son of Anor.

Reveal 2x The Necromancer's Reach (Gimli gains a resource when the Son of Anor dies (total of 3), Gloin gains 2 resources, 14 total damage on heroes)
Reveal Goblin Sniper

Play 2x Sneak Attack to put Gandalf (deal 4 damage to Hill Troll, 1/9 HP remaining) and Son of Anor (engage Goblin Sniper) into play.

Play Blade Mastery to give Legolas +1 Attack
Play Quick Strike and have Legolas ranged attack the Hill Troll, defeating it and adding 4 progress to the quest.
Ready with Unexpected Courage
Play Quick Strike and have Legolas ranged attack the Goblin Sniper, defeating it and completing Stage 1.

Resolve the quest, adding 16 progress and completing stage 2.

Reveal 6 locations for the Forced effect on Stage 3, completing the quest!