3) Put great whale onto the battlefield using sneak attack and untap 7 lands. Make sure when you untap lands you have a healthy mix of black, blue, and red mana. Do not lopside it otherwise you may not have the correct mana left open to win the challenge with. I would suggest 3 red and 3 blue alongside whatever black.
1) Buyback Demonic Collusion twice, discarding brainspoil, coercion, infernal tutor, and betrayal of flesh. Grab great whale and spitting image with your collusions.
2) Then cast Demonic Collusion non-buyback to grab past in flames.
3) Put great whale onto the battlefield using sneak attack and untap 7 lands. Make sure when you untap lands you have a healthy mix of black, blue, and red mana. Do not lopside it otherwise you may not have the correct mana left open to win the challenge with. I would suggest 3 red and 3 blue alongside whatever black.
4) Cast spitting image targeting your great whale to untap lands.
5) Cast past in flames. Flashback brainspoil targeting your non-token great whale.
6) Flashback betrayal of flesh without entwine to return great whale from your graveyard to the battlefield to untap lands.
7) Flashback infernal tutor to grab snap. Cast snap targeting your non-token great whale and untap two lands.
8) Use sneak attack to put great whale onto the battlefield and untap lands.
9) Flashback spitting image and put a token of great whale onto the battlefield and untap lands.
10) Flashback both of your Demonic Collusions without buyback to grab hoodwink and tendrils of agony.
11) Cast hoodwink to return your opponent's Leyline of Sanctity to their hand.
12) Then cast tendrils of agony to target your opponent and all copies of it targeting your opponent as well.
13) Flashback past in flames making sure to leave a U mana open at least.
14) Flashback snap, untap two lands making sure you have a R open, to return your non-token great whale to your hand.
15) Use sneak attack to put great whale onto the battlefield and untap lands and at this point you no longer need red mana and at least 4 black mana.
16) Flashback coercion to discard your opponent's Leyline of Sanctity.
17) Flashback hoodwink to return your helm of awakening to your hand, then recast the helm.
18) Flashback tendrils of agony targeting your opponent with it and all copies.
Congrats, you have solved this challenge!