Démon aux noirs desseins

The set of creatures affected by Demon of Dark Schemes's first triggered ability is determined as the ability resolves. Creatures that enter the battlefield later in the turn and noncreature permanents that become creatures later in the turn won't get -2/-2.
Demon of Dark Schemes's second triggered ability triggers whenever another creature dies for any reason, not just due to the first triggered ability.
If Demon of Dark Schemes dies at the same time as another creature, its second triggered ability triggers.
If a creature's owner leaves the game after you've put that creature onto the battlefield with Demon of Dark Schemes's last ability, the creature leaves with that player. If you leave the game before that player, the creature is exiled.
Keep careful track of how many energy counters each player has. You may do so by keeping a running count on paper, by using a die, or by any other clear and mutually agreeable method.
is the energy symbol. It represents one energy counter.
You can't pay more energy counters than you have.
Energy counters aren't mana. They don't go away as steps, phases, and turns end, and effects that add mana “of any type” to your mana pool can't give you energy counters.
If an effect says you get one or more , you get that many energy counters. To pay one or more , you lose that many energy counters. Any effects that interact with counters a player gets, has, or loses can interact with energy counters.
Energy counters are a kind of counter that a player may have. They're not associated with specific permanents. (Other kinds of counters that players may have include poison and experience.)