Charles Ellicott Commentary 2 Kings 21:6

"And he made his son to pass through the fire, and practised augury, and used enchantments, and dealt with them that had familiar spirits, and with wizards: he wrought much evil in the sight of Jehovah, to provoke him to anger." — 2 Kings 21:6 (ASV)

And he made his son ... —The Septuagint has his sons; as does Chronicles.

Dealt with familiar spirits ... —made a necromancer —that is, formally appointed such a person as a court official (1 Kings 12:31). (See the Notes on chapters 16:3, 17:17, and especially 2 Chronicles 33:6.)

“In the time from Manasseh onwards, Moloch-worship and worship of the Queen of Heaven appear as prominent new features of Judah’s idolatry. It is also probable that the local high places took on their restoration a more markedly heathenish character than before” (Prof. Robertson Smith).