Tekuthal, Inquiry Dominus doubles your proliferate actions, giving blue counter decks two proliferations whenever they would normally perform one. Each proliferation is a separate event, allowing existing loyalty, charge, +1/+1, poison, and other counters to advance more quickly. The flying body adds a defensive and offensive presence while the replacement effect improves the deck's counter engines.
Evolution Sage in a blue-green deck turns land entries into repeated proliferation, while Flux Channeler can reward noncreature spells in a spell-heavy build. Planeswalker decks can use the additional loyalty counters to reach useful activations sooner. The two proliferations do not have to choose exactly the same permanents or players, giving you flexibility when some counters are helpful and others are not.
Tekuthal can gain an indestructible counter by paying its activation cost and removing three counters from among other artifacts, creatures, and planeswalkers you control. Those removed counters are a real cost, so use counters that are expendable or can be rebuilt. Counters on Tekuthal itself cannot pay that particular removal requirement.
Proliferate cannot place the first counter of a new kind on an object that does not already have it. The deck therefore needs ways to establish useful counters before Tekuthal amplifies them. Indestructible also leaves exile, bounce, and sacrifice answers available. Build a counter engine that remains functional without the Dominus, then use its doubling effect to accelerate an already productive board.
