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.Drowned Catacomb supports blue-black decks by supplying either color from one land. It enters untapped when you already control an Island or a Swamp, so its performance depends on the types represented by your earlier land drops. A basic or a typed nonbasic can satisfy that requirement. This makes it particularly useful after the first turn, when the mana base has begun to establish itself.
Watery Grave is a useful partner because its basic land types can enable the untapped entry. Polluted Delta can find that shock land or an appropriate basic first, setting up a later Drowned Catacomb. Sequencing those sources in the right order can preserve mana for development and interaction without paying life for this land itself.
For control and reanimation strategies, the practical benefit is choosing between spells such as Entomb and Counterspell as the turn develops. Black setup spells can prepare a graveyard while blue interaction protects the eventual payoff. Reanimate and Animate Dead benefit from a mana base that can establish black early without cutting off later blue responses. A flexible source supports those decisions without requiring a separate fixing artifact to stay on the battlefield.
The entry check uses land types rather than names or the colors a land happens to produce. Drowned Catacomb has no basic land types of its own, so a fetch land cannot search for it. An opening hand built only from lands with similar conditions may start slowly. Keep enough reliable first-turn sources to make the condition easy to meet.
