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).

The Statement on Schedule
13D, as originally filed with the Securities and Exchange Commission (the SEC) on May 10, 2010, as amended by Amendment No.1 filed with the SEC on May 24, 2010, as further amended by Amendment No. 2 filed with the SEC on April 8,
2011, as further amended by Amendment No. 3 filed with the SEC on July 13, 2011, as further amended by Amendment No. 4 filed with the SEC on March 14, 2012, as further amended by Amendment No. 5 filed with the SEC on February 3, 2014, as further
amended by Amendment No. 6 filed with the SEC on October 27, 2015 and as further amended by Amendment No. 7 filed with the SEC on May 26, 2016 (collectively referred to as the Schedule 13D), by the Reporting Persons named therein
is hereby further amended and supplemented by this Amendment No. 7 to Schedule 13D. Capitalized terms used herein and not otherwise defined have the meanings assigned to such terms in the Schedule 13D.

The information set forth in response to each separate Item below shall be deemed to be a response to all Items where such information is
relevant. The Schedule 13D is hereby amended as follows:

Page 6 of 8

Item 4. Purposes of Transaction.

Item
4 is hereby amended to add the following:

The Reporting Persons sold 5,060,628 shares of Common Stock to the Issuer on April 28, 2017.
Following this transaction, the Reporting Persons currently intend to hold their remaining stake of 8,500,000 shares of Common Stock. The Reporting Persons continue to be optimistic about the Issuers prospects.

Item 5. Interest in Securities of the Issuer.

Item 5 is hereby amended and restated in its entirety as follows:

The information set forth in Item 4 of this Statement is hereby incorporated by reference into this Item 5. As of April 28, 2017, the Reporting
Persons beneficially own an aggregate of 8,500,000 shares of Common Stock, or approximately 9.94% of the 85,549,339 shares of Common Stock outstanding as of April 21, 2017, as reported in the Issuers quarterly report on Form 10-Q for the
quarterly period ended March 31, 2017 (after giving further effect to the Issuers repurchase of shares from the Reporting Persons). These shares of Common Stock include shares of Common Stock received by the H Partners Entities in
connection with the Issuers emergence from bankruptcy and subsequently transferred between investment funds, and shares of Common Stock transferred to investment funds that are managed by H Management.

(a) and (b)

1) H LP
directly beneficially owns 5,552,683 shares of Common Stock, constituting approximately 6.49% of the Common Stock outstanding. As of the date of this filing, H LP has sole voting power and sole investment power with respect to all the shares of
Common Stock referred to in the previous sentence.

2) H Capital, as the general partner of H LP, may be deemed to beneficially
own 5,552,683 shares of Common Stock, constituting approximately 6.49% of the Common Stock outstanding. H Capital may be deemed to have sole voting power and sole investment power with respect to all the shares of Common Stock referred to in
the previous sentence.

3) H Management, as the investment manager of H Capital, H Offshore and Phoenix Capital, may be deemed
to beneficially own 8,500,000 shares of Common Stock, constituting approximately 9.94% of the Common Stock outstanding. H Management may be deemed to have sole voting power and sole investment power with respect to all the shares of Common
Stock referred to in the previous sentence.

4) Jaffer, as the managing member of H Management, H Capital and Phoenix Capital,
may be deemed to beneficially own 8,500,000 shares of Common Stock, constituting approximately 9.94% of the Common Stock outstanding. Jaffer may be deemed to have sole voting power and sole investment power with respect to all the shares of Common
Stock referred to in the previous sentence.

Neither the filing of this Statement nor any of its contents shall be deemed to constitute an
admission that any Reporting Person is the beneficial owner of any Common Stock referred to in this Statement for the purposes of Section 13(d) of the Act or for any other purpose, and such beneficial ownership is expressly disclaimed.

(c) Except as stated in Item 3 and Item 4 herein, there have been no other transactions in the securities of the Issuer effected by the
Reporting Persons in the last 60 days.

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(d) Except as stated within Item 4 and Item 5 of this Statement, to the knowledge of the Reporting Persons, only the Reporting Persons have the
right to receive or the power to direct the receipt of dividends from, or proceeds from the sale of, the shares of Common Stock of the Issuer reported by this Statement.

Item 7. Material to be Filed as Exhibits

Item 7 is hereby amended and restated in its entirety as follows:

Page 8 of 8

SIGNATURES

After reasonable
inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

EXHIBIT INDEX