The old Markdown Manager can now be found in Seller Hub>Marketing tab>Create Discount (blue button, with dropdown)> Sale Event.
"Sale Event" is basically "Markdown Manager". The biggest difference is that it no longer has the ability to create a tiered discount, such as 20% off these items, 10% off these other items, etc. You can run one discount per Event. So, now, if you want to do do 10% off some stuff and 20% off other stuff, you need to create two "sales events". I have a thread about this on the Board somewhere, but it has probably dropped off the front page.
