How effective is Wind against Dark and Grass?

That multiplier is the reason you keep a Wind attacker on the bench even when the rest of your team covers everything else. Against a target carrying both Dark and Grass, a Wind hit lands as high damage rather than ordinary damage, and it does so without any setup: no stacks to build first, no debuff count to reach, no window to hit. You bring the Wind unit in and the number is already there.

The practical use is picking who swings, not building around a gimmick. If a Dark and Grass Aniimo is the thing standing between you and the end of a fight, the Wind slot is the answer, and anything you were saving for burst is better spent behind it.

Where Dark and Grass targets turn up

Dark forms are gated. Darklers and the Umbrabow form come exclusively out of Egg Heist, and the currency you accumulate there can also be exchanged directly for an Umbrabow egg. The Dark half of this pairing is not something you stumble into in ordinary play, so the Wind matchup matters most around Egg Heist content and against anyone fielding what they pulled from it.

The element list is not fixed yet

Element counts still move between builds. The roster appears as nine elements covering Light, Dark, Fire, Wind, Water, Ice, Grass, Earth and Lightning or Electric, as ten with Rock added, and in another arrangement as Fire, Ice, Water, Grass, Electricity, Rock, Wind, Dark and Holy. Light and Holy, Lightning and Electricity, are the same slot wearing different names. Treat any full chart you build as provisional. The Wind figure against Dark and Grass is concrete. The shape of the grid around it is not.

Not settled: The 2.56 figure is given for the Dark and Grass dual type specifically. What Wind does against a single-type Dark or a single-type Grass Aniimo is not established, so you cannot read the individual matchups out of this one number.