If I have Thought Reflection and Asmodeus the Archfiend, what happens when I would draw a card? Can I order the replacement effects, both apply (i.e., Asmodeus exiles two cards), or something else?
When you would draw a card here, you have two replacement effects that both want to apply to that draw. Since neither of them take priority, you can apply either one first.
If you apply Asmodeus's effect first, then you would exile the top card of your library instead of drawing a card. Since you're no longer drawing any cards, Though Reflection no longer applies and you'll just exile the top card of your library.
If you apply Thought Reflection's effect first, then you would draw two cards. Since there's nothing waiting to modify the multiple draw, the game then parses it down into two individual draws. Asmodeus's effect will then be applied to each draw and exile a card from the top of your library twice instead.
TL;DR: You have your choice of exiling one or two cards here.
