interaction - chains of mephistopheles and the dredge mechanic

[Purple Hat]

If I have a chains of mephistopheles in play against dredge what happens?  on my opponent's upkeep he taps bazaar and chains and dredge both trigger and as I understand it my opponent would then choose which effect he wants to have happen.  if he chooses to dredge he replaces the draw with the dredge effect and chains doesn't trigger.  if he chooses to discard to chains he can then dredge the subsequent draw.

is that correct?

Thanks.

[Clariax]

Very close...

Nothing triggers.  Chains and Dredge both involve exclusively static abilities.  Each ability sets up a replacement effect.  Since multiple replacement effects attempt to replace the same event (drawing a card), the affected player (person drawing the card in this case) chooses which replacement to apply first.  Then, after applying that first replacement effect, if any other replacement effects still apply to the event, they're applied.  (Again, if multiple replacement effects apply, affected player chooses which to apply first).

So, if, in the case given, dredge is applied first (and used), then there is now no draw, so Chains' replacement effect no longer applies.  If Chains' replacement effect is applied first, and a card is discarded to it, there's still a "Draw a card" event, which can then be replaced by dredging