Altar of the Brood turns every other permanent entering under your control into a mill effect for each opponent. Lands, creatures, artifacts, enchantments, and tokens can all contribute, giving the one-mana artifact a broad range of partners. A normal development turn creates small amounts of mill; a repeatable entry loop can turn that modest trigger into a finishing plan.
Blink engines and recurring token sequences are natural ways to increase the count. A creature repeatedly entering through a supported loop triggers the Altar each time, while a large token spell can create many triggers at once. The Altar does not need the entering permanent to have been cast, so reanimation and other direct battlefield effects qualify.
Milling a library is not identical to immediately winning. An opponent normally loses when they must draw from an empty library, and some cards can shuffle a graveyard back into the library or replace what happens when milled. Opponents with graveyard engines may also benefit from smaller, nonlethal amounts of mill. That makes the Altar more compelling when your deck can produce enough entries to threaten a decisive result or has a separate reason to fill opposing graveyards. Know the endpoint of the sequence and the interaction that could interrupt it; a low-cost permanent can be a strong combo payoff without being a strong standalone source of pressure in every game.
