Sentry Conduit

The Sentry Conduit guards your yard with your lens: it turns its bracer toward a monster within 12 blocks and casts at it while it sees it. With a Mend lens it is a healer at the gate: it heals your wounded — players, tamed animals, villagers — and, with none of them hurt, burns the undead. Use a cut lens on it to set it, sneak-use empty-handed to take it out, use it empty-handed to see what it is doing; only its owner touches the lens.

It takes flux from its own chunk by the rules of a cast: the lens's price, strength by how dry the place is, a weak cast and a fizzle at the bottom; murk as the lens blank leaves it. It never changes blocks: lenses with Survey, Excavate, Swap or Washout do not fit it, nor do traceries. Jet, Droplet and Moth strike as a beam, Palm point-blank, Mist and Pool as a flash of a circle at the target, Spray at several targets, Fork hops, Echo repeats at half strength. It casts at most once a second; sentries heal one wounded friend at most once a second, however many of them stand there.

The sentry sleeps while no player is within 64 blocks and under a redstone signal: no searching, no flux. Awake, it looks for a target twice a second and hears like the Keen Arbalest: a step or a voice in its circle — and the bracer has already turned. It never strikes its owner or your own: its targets are monsters only, and it leaves calm endermen and zombified piglins alone. What it kills gives no experience — as with an arbalest's arrows.