Does Leyline of the Void affect cards that would be put into the graveyard as a cost?

Leyline of the Void reads that if a card would be put into an opponent's graveyard from anywhere, exile it instead. However, this replacement effect only applies when a card is being put into a graveyard as part of a game action or effect — it does not intercept the payment of costs.

According to CR 117.1 and CR 118.9, paying costs (such as discarding a card, sacrificing a permanent, or milling yourself as a cost) happens as a special action during the process of activating or casting something. Costs are not 'effects' and are not subject to replacement effects in the same way a resolution effect moving cards would be. CR 614.1 specifies that replacement effects modify events, and cost payments are not events in the replaceable sense — they are simply executed.

More precisely, CR 117.3 states that some costs involve putting cards into the graveyard (e.g., discarding). When you pay such a cost, the card moves directly as part of cost payment — Leyline of the Void's replacement effect does not apply to intercept this movement, because replacement effects apply to game events generated by effects or rules, not to cost payments themselves.

Concrete example: You control Leyline of the Void. Your opponent activates Faithless Looting, then pays its flashback cost and discards two cards. Those two discarded cards go directly to your opponent's graveyard — Leyline of the Void does NOT exile them, because discarding as a cost is not an effect being replaced.

Note: once a card is in the graveyard and something would move it there again (e.g., via a triggered ability or spell effect), Leyline would apply. The distinction is purely: costs bypass replacement effects; effects do not.