Brine Elemental
Creature — Elemental
Morph 
(You may cast this card face down as a 2/2 creature for 
. Turn it face up any time for its morph cost.)
When this creature is turned face up, each opponent skips their next untap step.
Water calls to water, and the world is left exhausted and withered in its wake.
Stephen Tappin
Rulings
If an effect says that something doesn't untap during its controller's next untap step, that effect applies to the next untap step that isn't skipped.
(wotc • 2021-03-19)
Skipping your "next" untap step is cumulative. If a player turns two Brine Elementals face up on the same turn, that player's opponents will each skip their next two untap steps.
(wotc • 2021-03-19)
Printings
Rulings
If an effect says that something doesn't untap during its controller's next untap step, that effect applies to the next untap step that isn't skipped.
(wotc • 2021-03-19)
Skipping your "next" untap step is cumulative. If a player turns two Brine Elementals face up on the same turn, that player's opponents will each skip their next two untap steps.
(wotc • 2021-03-19)