Is this a peel off masque?

Paula, no it is not and therefore very convenient to use. With the face very slightly damp, the "cream" is applied a little at a time until all is covered. A wait time of no more than 15 minutes is needed. I apply the masque before I shower, wait the 15-20 minutes and then wash same off while showing; very convenient. I use once a week, very happy with the results, one jar as shown will last several weeks/months. Best, Craig.

Does this include mask and cleanser? Or just only mask? Thanks.

This is just a clay mask. Kiehl's, however, does make a cleanser from the clay as well, but that is a separate item.

Product is genuine it?

I really like it! it really tigthens up my pores. gets rid of blackheads and just you generally feel so clean after. Its not a miracle product be its defiantely great and worth the money

Can I wear this mask overnight ?

I wouldn't - it's a clay mask and will probably dry your skin severely if you leave it on for too long. You could probably do this with some hydrating masks, but not with a clay mask.