Exodus 10

2 witnesses of Christ here.

Jehovah

And the LORD said unto Moses, Go in unto Pharaoh: for I have hardened his heart, and the heart of his servants, that I might shew these my signs before him: Exodus 10:1–3

Jehovah tells Moses the signs in Egypt are meant to be retold to children and grandchildren so every generation knows Him. The premortal Christ wants families to pass down their testimony of His deliverance.

VerifiedJehovah — the LORDHe speaks in the first person

How we know: the verse itself names Him · another scripture interprets it of Him · a footnote points to Him

alluded to by Exodus 12:26-27 — The same picture of children asking and parents telling returns with the Passover: 'What mean ye by this service?'
alluded to by Exodus 13:14 — Again a son asks, and the father tells how 'by strength of hand the LORD brought us out.'

Three days of darkness (sign of His death)

And the LORD said unto Moses, Stretch out thine hand toward heaven, that there may be darkness over the land of Egypt, even darkness which may be felt. Exodus 10:21–23

Egypt sat in a darkness that could be felt for three days while the Lord's people had light. It softly echoes the three days of thick darkness in the Americas at Christ's death, and reminds us that those who follow Him have light.

VerifiedEchoAn echo of Him

How we know: a footnote points to Him

alluded to by 3 Nephi 8:20-23 — At the Savior's death, darkness that could be felt ('the vapor of darkness') lasted 'for the space of three days'; Church footnote 21b links the two.