"Sharp arrows of the mighty, with coals of juniper" (120:4). Are these what the deceitful tongue will be given, or what the tongue is like?

The verse doesn't say. Here is what the text shows. The line before asks the tongue, "What will be given to you, and what will be done more to you, you deceitful tongue?" (Psalm 120:3), and 120:4 comes straight after it. Elsewhere in the Psalms arrows and coals come upon the wicked from God, or are prayed for: "But God will shoot at them. They will be suddenly struck down with an arrow" (Psalm 64:7), and "Let burning coals fall on them" (Psalm 140:10), with 120:4's Hebrew word for coals. Other verses liken a tongue, or a false witness, to an arrow: "Their tongue is a deadly arrow. It speaks deceit" (Jeremiah 9:8), and "A man who gives false testimony against his neighbor is like a club, a sword, or a sharp arrow" (Proverbs 25:18), where sharp arrow is the same two Hebrew words as Sharp arrows in Psalm 120:4, singular there. Psalm 64 has both in one psalm: people "who sharpen their tongue like a sword, and aim their arrows, deadly words" (Psalm 64:3), and then God's arrow (Psalm 64:7). These notes set the verses side by side, and don't choose between reading Psalm 120:4 as what the tongue will be given and reading it as what the tongue is like.