Hearthpwn

Radiant Elemental and Prophet Velen are both dead -> Lesser Diamond Spellstone (7 mana) -> Vivid Nightmare on Radiant Elemental (2 mana) -> Vivid Nightmare on Prophet Velen (1 mana) -> Mind Blast x 2 (0 mana) = 40 damage

Basically, the combo relies on killing off a Radiant Elemental and a Prophet Velen, collecting the combo pieces and making sure that Lesser Diamond Spellstone can revive both Radiant Elemental and Velen. Keep in mind that reviving a Bloodmage Thalnos as well increases your burst potential (eg. 24 damage mind blast instead of 20). You can guarantee the revives with relative ease because the spellstone can resurrect up to 4 minions and this deck runs only 4 minions.

The true potential of this deck lies in its flexibility. In fact, there are multiple ways for you to close out the game with 40+ damage. There are also instances where you can play your other Radiant Elemental before the Lesser Diamond Spellstone, reviving a Radiant Elemental and a Prophet Velen for 8 mana. With the leftover 2 mana, you can:

a) Vivid Nightmare on Velen (1 mana) -> Mind Blast x 2 (0 mana) = 40 damage

b) Vivid Nightmare on Velen x 2 (2 mana) -> Mind Blast (0 mana) = 40 damage

Now, consider this best-case scenario:

All 4 minions dead, fully upgraded spellstone in hand -> Radiant Elemental (2 mana) -> Lesser Diamond Spellstone (6 mana) -> Vivid Nightmare on Velen (1 mana) -> Vivid Nightmare on Velen (1 mana) -> Mind Blast x 4 (2 from Shadow Visions) (0 mana) = 192 damage!!!

There is no deck in the current Standard meta that can withstand this metric ton of damage (RIP Ice Block, also no one actually runs Evasion in their decks). In fact, most decks fail to survive 40 damage. You can pull off this combo very consistently with your heavy draw and multiple board clears (some of which double as healing). Furthermore, this revive-centric combo allows you to play your combo minions proactively; you can use Velen with a Spirit Lash to clear a wide board and heal back to full without disrupting your combo. You can also play a Radiant Elemental on turn 2 to contest for board early. The possibilities are endless.

Found here: https://www.reddit.com/r/CompetitiveHS/comments/8c98za/an_otk_with_short_animations_4_to_legend_velen/

It's a better version of the Vivid Nightmare's combo I predicted in march, which used Eternal Servitude instead of Spellstone:

https://www.hearthpwn.com/decks/1055059-theorycraft-vivid-nigthmare-otk-velens-version