Rainworn Gate

The cost cut does nothing by itself. It matters because Water’s removal checks cost: Back Alley Abductor, Gabu displaces cost 2 or less, Tidal Wave cost 3 or less, and Lotus of the Mizuryuu bottom-decks a combined cost of 3. Portal a Gate Power 2 entity and their 4-cost entity counts as 2 for Gabu, or a 5-cost one as 3 for Tidal Wave. Drowncalling Siren checks base cost, so the cut doesn’t widen its reach.

The cut lasts until the end of your opponent’s next turn, which ends before your next turn starts, so displace the entity the same turn you portal. A Gate Power 0 entity, like Sentinel of Passage, Usui, lowers nothing.

Timing: a card finishes resolving before the cards it triggers (Card Resolution Order), so the Gate’s cut lands before Gabu’s displace. Portal Gabu itself (Gate Power 2) and a 4-cost entity counts as 2 by the time Gabu picks its target.

Most Water entities have Gate Power 1 or 2. Gate Power 2: Gabu, Submerging Tides, Inoe, Backstreet Ratter, Vessel of Mizuryuu, Torrentstep Provoker, Kōga and Relic Runner Shao. Gate Power 1: the Siren and Gathering Tide, Rowan. Under Hei Lian, every displace this enables also turns on her +1 Attack.

From the full set, Puddle Abduction displaces cost 4 or less, so after a Gate Power 2 portal it reaches a 6-cost entity. Vessel of Mizuryuu bottom-decks cost 4 or less, and Water Prison returns cost 4 or less.