When you set this scheme in motion, target opponent chooses self or others. If that player chooses self, this scheme deals 6 damage to that player. If the player chooses others, this scheme deals 3 damage to each of your other opponents.
The Fate of the Flammable is not legal in any format.
The targeted player may choose "self" even if they can't perform the resulting action. For example, a player targeted with Feed the Machine may choose "self" even if they control no creatures.
The targeted player may choose "others" even if there are no others (because all of their teammates have lost the game, for example), or the archenemy's other opponents can't perform the resulting action.
In a Supervillain Rumble game, the targeted player may still choose "others." Each player who isn't the active player or the targeted player will thus be affected.