At the start of each game, the tide is neutral (neither high nor low). When either player raises the tide, the tide becomes high for them and low for their opponent. If the tide is already high for a player, they cannot raise the tide.
During the active player’s turn, they may use the ability “Omni: Raise the tide. Gain 3 chains.” This ability is granted by the game rules and not by a card ability. Unlike most “Omni:” abilities, this ability does not require a player to exhaust any card. A player can use this ability any number of times in a turn.
Each Dark Tidings Archon deck comes with a Tide reference card to help players track whether the tide is high or low for them, and to serve as a reminder that they have access to the “Omni:” ability to raise the ride. This card is only for reference, and never counts as a card in play or under a player’s control. When a card effect instructs a player to raise the tide, they should rotate the Tide reference card such that the side labeled “High Tide” is facing them and the side labeled “Low Tide” is facing their opponent.
Card abilities that refer to the tide are indicated by this icon:
Yes, now that the tide is integrated into the rules, you can take chains to raise the tide, turning off your opponent's Valoocanth, even if it is the anomaly version from Worlds Collide and neither of you are playing Dark Tidings decks.
That is one of the rare instances where taking the tide could have a game impact even if neither deck is from Dark Tidings. The other instance is when a player really doesn't want to draw cards and have to cycle through their deck, so they might arbitrarily raise the tide just to gain chains.Source
If I'm playing a Call of the Archons deck against a Worlds Collide deck that has the Anomaly version of Valoocanth, can I raise the tide to prevent Valoocanth from reaping even though neither of us is playing a deck with a Tide card?
That is one of the rare instances where taking the tide could have a game impact even if neither deck is from Dark Tidings. The other instance is when a player really doesn't want to draw cards and have to cycle through their deck, so they might arbitrarily raise the tide just to gain chains.