The key to this puzzle lies in getting a face-down 2/2 creature onto the battlefield for as few mana as possible, mostly because you need to save your resources for the spells that really count. On top of that, your Icefeather Aven won’t be able to win the game by itself; you’ll need to get the Gurmag Swiftwing onto the battlefield to help out.

1. Finish resolving your Sultai Ascendancy’s ability: Choose to return both cards to the top of your library, placing the Ruthless Ripper on top of the Gurmag Swiftwing.
2. During your draw step, draw the Ruthless Ripper.
3. At the beginning of your first main phase, tap three islands to add (all used as generic mana), two forests to add (one used as generic mana), and three swamps and a Jungle Hollow to add to your mana pool.
4. Spend to cast Ancestral Vengeance on your Sultai Emissary. When Ancestral Vengeance enters the battlefield, choose to put a +1/+1 counter on Icefeather Aven. Icefeather Aven is now a 3/3 creature.
5. Sultai Emissary is now a 0/0 creature, and dies. You now have two cards in your graveyard: Sultai Emissary and Ancestral Vengeance.
6. Sultai Emissary’s ability triggers, causing you to manifest the top card of your library (the Gurmag Swiftwing). Put Gurmag Swiftwing onto the battlefield as a face-down 2/2 creature.
7. Spend to attach Ghostfire Blade to the face-down Gurmag Swiftwing. (You can do this because the Swiftwing is a colorless creature as long as it is face-down.) The face-down Gurmag Swiftwing is now a 4/4 creature.
8. Spend to cast Savage Punch, targeting your face-down Gurmag Swiftwing and Lucienne’s Sage-Eye Harrier. Because your face-down Swiftwing is a 4/4 creature, Savage Punch gives it +2/+2 until end of turn. The face-down Gurmag Swiftwing is now a 6/6 creature.
9. The Gurmag Swiftwing and the Sage-Eye Harrier deal damage to each other. The Harrier is dealt 6 damage and dies; the Swiftwing is dealt 1 damage and lives. You now have three cards in your graveyard: Sultai Emissary, Ancestral Vengeance, and Savage Punch.
10. Spend and exile all three cards from your graveyard to cast Murderous Cut on Lucienne’s Archfiend of Depravity, destroying it.
11. Spend to turn your face-down Gurmag Swiftwing face-up. Your Gurmag Swiftwing is now a 1/2 creature with flying, first strike and haste. It has Ghostfire Blade attached (giving it +2/+2), and it has the +2/+2 bonus from Savage Punch, making it a 5/6 creature in total.
12. Declare the start of your combat phase, assigning Icefeather Aven (3/3) and Gurmag Swiftwing (5/6) to attack.
13. Lucienne no longer has any flying creatures, and is unable to block your attackers. Your Aven and Swiftwing deal a total of 8 damage to Lucienne, defeating her.