Specimen Common Stock Certificate

Exhibit 4.2

Mount Rainier Acquisition Corp.

 INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE 
COMMON STOCK

This Certifies that

is the owner of

FULLY PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK, PAR VALUE $0.0001 OF

Mount Rainier Acquisition Corp.

(THE “COMPANY”)

transferable on the books of the Company in person or by duly authorized attorney upon surrender of this certificate properly endorsed.

The Company will be forced to redeem all of its shares of common stock if it is unable to complete a business combination by [•], 2023 (or such later date as the Company’s amended and restated certificate of incorporation may be amended to provide for), all as more fully described in the Company’s final prospectus dated [•], 2021.

This certificate is not valid unless countersigned by the Transfer Agent and registered by the Registrar.

Witness the seal of the Company and the facsimile signatures of its duly authorized officers.

Chief Executive Officer Chief Financial Officer

Mount Rainier Acquisition Corp.

The Company will furnish without charge to each stockholder who so requests a statement of the powers, designations, preferences and relative, participating, optional or other special rights of each class of stock or series thereof of the Company and the qualifications, limitations, or restrictions of such preferences and/or rights. This certificate and the shares represented thereby are issued and shall be held subject to all the provisions of the Company’s amended and restated certificate of incorporation and all amendments thereto and resolutions of the Board of Directors providing for the issue of securities (copies of which may be obtained from the secretary of the Company), to all of which the holder of this certificate by acceptance hereof assents. The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:

Additional abbreviations may also be used though not in the above list.

For value received,                    hereby sells, assigns and transfers unto

(PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER(S) OF ASSIGNEE(S))

(PLEASE PRINT OR TYPEWRITE NAME(S) AND ADDRESS(ES), INCLUDING ZIP CODE, OF ASSIGNEE(S))

shares of the common stock represented by the within Certificate, and hereby irrevocably constitutes and appoints

Attorney to transfer the said shares of common stock on the books of the within named Company with full power of substitution in the premises.

NOTICE: THE SIGNATURE(S) TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS WRITTEN UPON THE FACE OF THE CERTIFICATE IN EVERY PARTICULAR, WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATEVER.

THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM, PURSUANT TO S.E.C. RULE 17Ad-15 (OR ANY SUCCESSOR RULE).

In each case, as more fully described in, and subject to the terms and conditions described in, the Company’s final prospectus dated [•], 2021, the holder(s) of this certificate shall be entitled to receive a pro-rata portion of certain funds held in the trust account established in connection with the Company’s initial public offering only in the event that (i) the Company redeems the shares of common stock sold in the Company’s initial public offering and liquidates because it does not consummate an initial business combination by [•], 2023 (or such later date as the Company’s amended and restated certificate of incorporation may be amended to provide for), (ii) the Company offers to redeem the shares of common stock sold in its initial public offering properly submitted in connection with a stockholder vote to amend the Company’s amended and restated certificate of incorporation (A) to modify the substance or timing of the Company’s obligation to allow redemption in connection with the Company’s initial business combination or certain amendments to the Company’s certificate of incorporation prior thereto or to redeem 100% of such common stock if it does not consummate an initial business combination by [•], 2023 or (B) with respect to any other provision relating to stockholders’ rights or pre-initial business combination activity, and the holder(s) of this certificate elects to have the shares of Common Stock held by him, her or it redeemed pursuant to that offer, or (iii) if the holder(s) seek(s) to redeem for cash his, her or its respective shares of common stock in connection with a tender offer (or proxy solicitation, solely in the event the Company seeks stockholder approval of the proposed initial business combination) setting forth the details of a proposed initial business combination. In no other circumstances shall the holder(s) have any right or interest of any kind in or to the trust account.