Can you use Necropotence's exile replacement effect to avoid drawing from an opponent's forced draw effect?

Necropotence has a replacement effect (CR 614.1) that reads: 'If you would draw a card, exile that card face down instead.' This is a self-replacing effect — it applies whenever you would draw a card, regardless of the source of that draw effect. So yes, it actually does replace draws forced by opponents too.

CR 614.1a explains that replacement effects modify how an event occurs. Since Necropotence says 'if you would draw a card,' it intercepts any draw event that would cause you to draw — including ones your opponent initiates (e.g., a spell that says 'target player draws two cards' targeting you).

The key nuance: Necropotence replaces the draw entirely with exiling the card face down. You do NOT draw the card at all. Instead, it goes to exile, and you may pay 1 life at the beginning of your next end step to put it into your hand (the separate triggered ability on Necropotence).

So Necropotence does NOT help you 'avoid' the forced draw in the sense of doing nothing — the card still leaves your library. It just goes to exile instead of your hand. If your opponent plays a 'mill via draw' strategy or wants to deck you, Necropotence actually changes where the card goes but your library still shrinks.

Example: Your opponent targets you with Prosperity for X=3. Normally you'd draw 3 cards. With Necropotence out, instead those 3 cards are exiled face down, and at the beginning of your next end step, you may pay 3 life to put them all into your hand.