Water Form. The elemental can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

Freeze. If the elemental takes cold damage, it partially freezes; its speed is reduced by 20 feet until the end of its next turn.

Raging River Form

Multiattack. The elemental makes two slam attacks.

Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 4) bludgeoning damage.

River Maiden Form

Spellcasting. This is an 5th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 14, +6 to hit with spell attacks). The lich has the following spells prepared:

Cantrips (at will): shape water

1st level (4 slots): create or destroy water

2nd level (3 slots):  detect thoughts, invisibility

3rd level (3 slots): wall of water, water walk, water breathing,  Tongues

4th level (2 slots): Watery Sphere, Control Water