The Outriders Expansion pack includes 34 new creatures and 6 new Unhallowed illustrated by Alexandr Elichev, one of the artists of Gloomhaven and Frosthaven. This expansion introduces a new game mechanic with Creatures that have the Rider ability. Riders snap together with certain creature types when they are adjacent to them, creating bigger and more powerful creatures (i.e. a Beast Rider card snaps and is placed over top any adjacent Forest Creatures). This shortening of the line can cause some additional creature powers to trigger. Leaving that Forest Creature in first position isn't as safe as it used to be!
This expansion is compatible with the original Set a Watch and Swords of the Coin.