The most reliable early manuscripts of the Gospel of Mark do not contain Mark 16:9–20, and the style of the Greek language used in these verses differs from the rest of Mark. This suggests that these concluding verses might not have been written by Mark, but rather by scribes who added accounts of the Savior’s appearances after His Resurrection

LDS New Testament Student Manual, Chapter 14
https://www.churchofjesuschrist.org/study/manual/new-testament-student-manual/introduction-to-mark/chapter-14?lang=eng

And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues; They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover.

Mark 16:17-18
https://www.churchofjesuschrist.org/study/scriptures/nt/mark/16.p17-p18?lang=eng#p17

And these signs shall follow them that believe—in my name shall they cast out devils; they shall speak with new tongues; they shall take up serpents; and if they drink any deadly thing it shall not hurt them; they shall lay hands on the sick and they shall recover;

Mormon 9:24
https://www.churchofjesuschrist.org/study/scriptures/bofm/morm/9.p24?lang=eng#p24