Getting my Grey Knights vibe going by taking a look at the latest for them in Psychic Awakening Ritual of the Damned. Time for me to dust them off? Possibly.
via the Warhammer Community
Rather than having the doctrines of the other Space Marines Chapters, this allows the Grey Knights to choose one of four different Tides to be dominant during the game. These give your entire army a bonus – choose the Tide of Fury if you want to easily cut your way through enemy forces.