Your knockback is reduced to zero, horizontally and vertically. A sword hit still hurts, it just no longer moves you.
On a soup server, knockback is what decides distance. A player pushed away loses contact, has to walk back in, and drinks on the way. The Anchor removes that breathing room: once you are glued on, you stay glued on.
The downside is complete. You can no longer use knockback to break away, nor be thrown out of a bad exchange. You take the fight you started, all the way.
Note from 03/09/2026 — the Slowness aura this page used to advertise has been removed from the kit. Stacking an area slow with knockback immunity would have made it the best kit on the server, with no counter.