Lunar Portal Staff

Unlike every other sentry this one hangs wherever you place it instead of dropping to the floor. That is not a convenience, it is the whole technique. Set it high and the sweeping beam rakes down across the ground beneath, covering an enormous cone. Set it at eye level and most of the same sweep points at the sky and the dirt.

It cuts through everything it touches with no falloff, which is why this is the sentry people bring to the Frost Moon and the pillars rather than to a single boss. A line of enemies walking into the sweep all take the same hit. Terrain stops it dead though, so a portal tucked behind a corner of your arena contributes nothing at all.

Two or three spread across an arena cover far more ground than the same number stacked together, since each only sweeps its own arc. Space them along the route enemies take instead of clustering them over your head. Your sentry cap from armor and potions is the real limit, and this is worth spending every point of it on.