# Yahweh once rejoiced over you ... multiplying you ... rejoice over you in making you perish and in destroying you. You will be plucked

Moses is speaking to the Israelites as a group, so all instances of "you" are plural.

# Yahweh once rejoiced over you in doing you good, and in multiplying you

"Yahweh once enjoyed doing you good and causing you to become many"

# he will rejoice over you in making you perish

"he will enjoy making you die"

# You will be plucked off the land that you are going into to possess

"He will remove you from the land which you are entering to possess" 

# you are going

Moses speaks to the Israelites as if they were one man, so the word "you" is singular.