dark smog, is it cost or effect?

I basically want to know if the continuous trap dark smog's 'discard' requirement is cost or effect. What I've found suggests its part of the effect, but the isn't a link to a ruling on the wikia. The card reads, "Once per turn: You can target 1 monster in your opponent's Graveyard; discard 1 Fiend-Type monster and banish that target." To me it sounds like the 'discard' is part of the card effect, but I wanted to make sure before I tried it in my dw deck since I HATE when people don't know the rules on cost vs effect for their abilities so I'm making sure I understand the card before I blindly put it in the deck.

The discard is part of the effect.

You pick the target first, then you discard your fiend and banish a monster from your opponents grave.

It is indeed an effect. Anything that comes after the semicolon on a card that has Problem Solving Card Text is an effect and not a cost.

"Once per turn: You can target 1 monster in your opponent's Graveyard; discard 1 Fiend-Type monster and banish that target."

Effect

This might help you for future cases:

http://yugioh.wikia.com/wiki/Problem-Solving_Card_Text