Turn Vesuvan Shapeshifter face-up for {1}{U}.
As it turns face up, have it copy Brine Elemental, triggering Brine Elemental's face-up ability.
Resolve the ability; each opponent skips their next untap step.
Pass the turn; on your upkeep, turn Vesuvan Shapeshifter face down.
Repeat infinitely.

Opponents skip their untap steps

Lock

Brine Elemental

Vesuvan Shapeshifter

Activate Isochron Scepter by paying {2} and tapping it, casting a copy of Backslide without paying its mana cost.
Resolve Backslide, turning Brine Elemental face down.
Activate Ixidor by paying {2}{U}, turning Brine Elemental face up.
Brine Elemental triggers, causing each opponent to skip their next untap step.
Repeat during each of your turns.

Combos with "Brine Elemental"