which one is correct?

Incredible as it may seem or incredible as it may seems?

please describe it for me.

Modal verbs such as “may” are always followed by the verb infinitive, so it should be “seem”.

In cases like this, you may find it helpful to substitute the verb “be”, because that has more distinctive forms for its parts. For example, you may know that “it may is” is wrong and “it may be” is correct. That will show you that the infinitive is needed.

Thanks a lot dear Dozy