If you use the link to sign up for a new account you will get 10% off commissions for 6 months.

I copied the text from this page:
https://www.bitmex.com/app/affiliates

Referred User Benefits
Users who have signed up with a valid affiliate link will receive a 10% fee discount for 6 months.

Fee structures may be different per contract; the discount will apply on all contracts. See the Fees Page to view the fee structure for a particular contract.