When filing an amended tax return, for a corrected W-2 or anything else, you are absolutely right that it must be printed and mailed, because amended returns cannot be e-filed (as a government rule). But there is often taxpayer confusion as to what exactly needs to be mailed. Hopefully this answer will help to clarify.
1) You must include all pages of Form 1040X (the amended tax return document)
2) Sending in your amended Form 1040 (not the original copy, but the copy that has been changed due to the process of amending the numbers) is sometimes considered optional. Some IRS personnel and tax professionals say to include it; others don't. To err on the side of caution, you may want to include the two pages of your amended Form 1040 simply to be complete, and that's what we would recommend in this answer.
3) You must include any other tax forms or schedules (other than the primary 1040) that contain information that is different from your original tax return. Basically, any document that has been changed, or has new numbers on it, needs to be included.
4) You should also send a true photocopy of any tax document that wasn't included in your original tax return. For example, if you amended your tax return because of your W-2, then you should include a photocopy of that, attached to the very back of your tax return. You don't need to send the original (or the original of the corrected W-2) with your amended tax return.
5) If your amended return reveals that you now owe the IRS more money, and if you decide to pay that bill by check or money order, also include that payment in your amended tax return envelope (but don't staple your payment to your amended return, just leave it loose in the envelope).
6) But do not include with your amended tax return, any forms or schedules that the IRS already has, and that have not changed at all from your original tax return (for example, if you added a W-2 to your return for wage income, but your taxable interest income hasn't changed, don't include a Schedule B with your amended return filing, because it is otherwise identical to what you reported on your original return).
With respect to your amended state income tax return (if any) the procedures vary. Some states have their own version of a state-level 1040X, others don't. You'll need to follow the state-specific guidelines as it applies to item # 1 above. But for items # 2 through # 6, you can safely follow the same advice for state amended returns as for federal amended returns.
Thank you for asking this important question.
