sb isn't optimal yet.
this is what i have been happy goldfishing with so far:
// 60 Maindeck
// 10 Artifact
4
Ruby Medallion4
Lotus Petal3
Helm of Awakening// 12 Instant
4
Seething Song4
Manamorphose4
Desperate Ritual// 14 Land
10
Mountain4
Ancient Tomb// 24 Sorcery
2
Past in Flames4
Rite of Flame4
Act on Impulse4
Burning Wish4
Gitaxian Probe3
Bonus Round2
Faithless Looting// 15 Sideboard
// 2 Instant
SB: 2
Abrade// 13 Sorcery
SB: 1
Past in FlamesSB: 1
Reforge the SoulSB: 1
Empty the WarrensSB: 1
GrapeshotSB: 1
Tendrils of AgonySB: 1
By ForceSB: 1
Cave-InSB: 1
PyroclasmSB: 1
Shattering SpreeSB: 1
GambleSB: 1
Dark PetitionSB: 1
Bonus RoundSB: 1
Banefire
also am considering a singleton gamble in the main over a faithless.
(banefire is pretty interesting, if you have a copy you only need to do it for 10, which isn't really so hard. it's probably overkill but it does get around glacial chasm for red and it will stop them if somehow they are able to counter your win con. it will very likely get cut, but putting it out there. could also very be a hazoret's in the sb.)
for an LED build i'd go with this:
// 60 Maindeck
// 12 Artifact
4
Ruby Medallion4
Lotus Petal4
Lion's Eye Diamond// 12 Instant
4
Seething Song4
Manamorphose4
Desperate Ritual// 14 Land
10
Mountain4
Ancient Tomb// 22 Sorcery
1
Past in Flames1
Empty the Warrens4
Rite of Flame4
Act on Impulse4
Burning Wish3
Gitaxian Probe3
Bonus Round1
Faithless Looting1
Gamble// 15 Sideboard
// 15 Sorcery
SB: 1
Past in FlamesSB: 1
Reforge the SoulSB: 1
Empty the WarrensSB: 1
GrapeshotSB: 1
Fiery GambitSB: 1
Tendrils of AgonySB: 1
By ForceSB: 1
Cave-InSB: 1
PyroclasmSB: 1
Shattering SpreeSB: 1
GambleSB: 1
Dark PetitionSB: 1
Bonus RoundSB: 1
BanefireSB: 1
Gitaxian Probe
it's possible cutting 1 pyroclasm or banefire could make sense to squeeze in a
hull breach.
also to answer this:
Not that this matters in practice because if you resolve a Bonus Round you've pretty much already won, but for the sake of amusement how many copies do you get for each subsequent Bonus Round? 1 BR = 1 copy; 2 BR = 3 copies?; 3 BR = 7 copies?; 4 BR = 15 copies?
it's the same as a binary sequence, but the number of copies will be one less that value.
1,2,4,8,16,32,64,128,256,512
you cast the first one and you get:
1 copy
3 copies
7 copies
15 copies
31 copies
63 copies
127 copies
255 copies
(after that you can't flash any more back).