(Amendment No.1) For the fiscal year ended:December 31,2024 OR ☐TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF1934 For the transition period fromto. Commission file number001-42157 SIX FLAGS ENTERTAINMENT CORPORATION (Exact name of registrant as specified in its charter) 93-4097909(I.R.S. EmployerIdentification No.) Delaware(State or other jurisdiction ofincorporation or organization) 8701 Red Oak Blvd.,Charlotte,North Carolina28217(Address of principal executive offices) (Zip Code) (704)414-4700(Registrant’s telephone number, including area code) Securities registered pursuant to Section12(b) of the Act: TradingSymbol(s)FUN Name of each exchangeon which registeredNew York Stock Exchange Title of each classCommon Stock,par value $0.01 per share Securities registered pursuant to Section12(g) of the Act: None Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.☒Yes☐No Indicate by check mark if the registrant is not required to file reports pursuant to Section13 or Section15(d) of the Act.☐Yes☒No Indicate by check mark whether the registrant (1)has filed all reports required to be filed by Section13 or 15(d) of the Securities Exchange Act of 1934during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2)has been subject to such filingrequirements for the past 90 days.☒Yes☐No Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 ofRegulationS-T(§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit suchfiles).☒Yes☐No Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, anon-acceleratedfiler, a smaller reporting company, or anemerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growthcompany” in Rule12b-2of the Exchange Act. Large accelerated filer☒Non-acceleratedfiler☐ Acceleratedfiler☐Smallerreportingcompany☐ Emerging growth company☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with anynew or revised financial accounting standards provided pursuant to Section13(a) of the Exchange Act.☐ Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internalcontrol over financial reporting under Section404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm thatprepared or issued its audit report.☒ If securities are registered pursuant to Section12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in thefiling reflect the correction of an error to previously issued financial statements.☐ Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensationreceived by any of the registrant’s executive officers during the relevant recovery period pursuant to§240.10D-1(b).☐ Indicate by check mark whether the registrant is a shell company (as defined in Rule12b-2of the Exchange Act).☐Yes☒No The aggregate market value of depositary units held bynon-affiliatesof Former Cedar Fair (as defined below) based on the closing price of such unitson June28, 2024 of $54.35 per unit was approximately $2,737,139,536. The aggregate market value of common stock of Former Six Flags (as defined below) held bynon-affiliatesbased on the closing price of such commonstock on June28, 2024 of $33.14 per share was approximately $2,366,835,569. Number of shares of the registrant’s common stock as of April 28, 2025:101,101,235shares None. ************Page 1 of 71 pages Table of Contents SIX FLAGS ENTERTAINMENT CORPORATION2024 FORM10-K/ACONTENTS Table of Contents PART IV ITEM 15 EXHIBITS AND FINANCIAL STATEMENT SCHEDULES SIGNATURES Table of Contents EXPLANATORY NOTE This Amendment on Form10-K/A(the “Amendment” or the “Form10-K/A”)amends the Annual Report on Form10-Kof Six Flags EntertainmentCorporation (the “Company”) for the year ended December31, 2024, as filed with the Securities and Exchange Commission (“SEC”) on March3, 2025(the “Original Form10-K”).This Amendment is being filed solely for the purpose of disclosing information required in Part III that the Company willnot be incorporating by reference to a definitive proxy statement. Noother parts or disclosures from the Original Form10-Kare included in thisAmendment other than Parts III and IV below, and except as required to reflect the matters set forth in such included disclosure, this Amendment doesnot reflect events or developments that have occurred aft