13D Filing: Rehan Jaffer and Six Flags Entertainment Corp (SIX)

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101. Information to be Included in Statements Filed Pursuant

to § 240.13d-1(a) and Amendments Thereto Filed Pursuant to § 240.13d-2(a))

Under the Securities Exchange Act of 1934

(Amendment No. 8)*

Six Flags
Entertainment Corporation

(Name of Issuer)

Common Stock, par value $0.025

(Title of Class of Securities)

83001A 102

83001A 201

(CUSIP Number)

H Partners Management, LLC

888 Seventh Avenue

29th
Floor

New York, New York 10019

Attn: Rehan Jaffer

212-265-4200

(Name,
Address and Telephone Number of Person Authorized to Receive Notices and Communications)

April 28, 2017

(Date of Event which Requires Filing of this Statement)

If the filing
person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or
240.13d-1(g), check the following box.  ☐

Note. Schedules filed in paper format
shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

*The remainder of this cover page
shall be filled out for a reporting persons initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be filed for the purpose of Section 18 of the
Securities Exchange Act of 1934 (Act), or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).