Helen may have control of your Nemesis of Mortals right now (not to mention, made it into a giant flying beacon of destruction), but at least it’s tapped. If you’re going for the win this turn, that makes a lot of difference ― mostly because Helen doesn’t have a way to untap it right now, and you can safely ignore it as a result.

You’ll also need a way to shut down the Eidolon of the Great Revel if you want to cast any of the cards in your hand. When you’re at four life, you don’t want to inadvertently knock yourself down to zero while struggling to make the best play.

Once that’s done, you can concentrate on getting past Helen’s many blockers. And now the real question comes to light: How?

1. Tap three forests to add GGG (two used as generic mana) and four plains to add WWWW to your mana pool.
2. Spend 1G to cast Nylea’s Presence on your Temple of Plenty.
3. When you cast Nylea’s Presence, the ability of Helen’s Eidolon of the Great Revel triggers, dealing 2 damage to you. You are now at 2 life.
4. When Nylea’s Presence enters the battlefield, three abilities trigger: the Constellation abilities of your Goldenhide Ox and your Oakheart Dryads, and your Nylea’s Presence.
5. Resolve Oakheart Dryads’ ability, choosing to give Goldenhide Ox +1/+1 until end of turn. Goldenhide Ox is now a 7/6 creature. (Note that the Ox already gets +1/+1 from your Spear of Heliod.)
6. Resolve Goldenhide Ox’s ability. Choose to require your Loyal Pegasus to be blocked this turn if able.
7. Resolve the ability of Nylea’s Presence and draw a card. You draw Gods Willing.
8. Spend 1WW and tap Spear of Heliod to activate its ability, targeting Helen’s Eidolon of the Great Revel. The Eidolon is destroyed.
9. Spend W to cast Chained to the Rocks on your Temple of Plenty. (Because of Nylea’s Presence, the Temple of Plenty counts as a Mountain, and can therefore be enchanted by Chained to the Rocks.)
10. When Chained to the Rocks enters the battlefield, choose to exile Helen’s Gold-Forged Sentinel.
11. Oakheart Dryad’s Constellation ability triggers. Choose to give Goldenhide Ox +1/+1 until end of turn. Goldenhide Ox is now an 8/7 creature.
12. Goldenhide Ox’s Constellation ability triggers. Choose to require your Griffin Dreamfinder to be blocked this turn if able.
13. Spend W to cast Gods Willing on your Goldenhide Ox, giving it protection from red until end of turn. Resolve the scry 1 ability as you choose.
14. Declare the start of your combat phase, assigning your Loyal Pegasus, Griffin Dreamfinder, and Goldenhide Ox to attack.
15. Because your Loyal Pegasus and Griffin Dreamfinder must be blocked, Helen must assign her War-Wing Siren and her Prescient Chimera to block these creatures (since none of her other remaining creatures are able to block these flyers).
16. Helen is unable to block your Goldenhide Ox with her Stormcaller of Keranos or Borderland Minotaur, since the Ox has protection from red. As a result, your Goldenhide Ox goes unblocked.
17. Your Goldenhide Ox deals 8 damage to Helen, defeating her.