Sinister Concoction

Oracle Text
, Pay 1 life, Put the top card of your library into your graveyard, Discard a card, Sacrifice Sinister Concoction: Destroy target creature.
Card Rulings
4/8/2016 You may pay Sinister Concoction’s costs in any order. However, once you’ve decided to activate the ability and you’ve seen the top card of your library, you can’t change your mind.
The milling and life loss are irrelevant. Just pretend it's a sorcery that costs BB and says "As an additional cost, discard a card. Destroy target creature." Yeah it's always a 2.5 for 1, but it's cheap and hits anything.
How is milling irrelevant in a set with Delirium? I'm intrigued.
This card is costing the player 5 resources for 1 effect.