Underground RiverHow it works & interactions with other cards

Versatile Mana Production

Underground River features two distinct activated abilities. The first ability taps for one colorless mana with no drawback. The second ability allows you to choose between adding one blue or one black mana, but it triggers a source of 1 damage to you as part of the resolution.

The Timing of Damage

When you tap Underground River for blue or black mana, the damage is dealt to you immediately as the mana is added to your pool. This is not a triggered ability that goes on the stack; it is part of the mana ability itself. Because it is damage, it can be prevented by effects that shield against damage, but it cannot be 'responded to' once you decide to activate the ability.

Common Misconceptions

A common mistake is treating the 1 damage as a cost. It is actually an effect of the ability. You do not need to have more than 1 life to activate it, though doing so at 1 life will cause you to lose the game when state-based actions are checked. Additionally, this damage does not count as 'loss of life' for effects that specifically look for life being paid as a cost.

Strategic Placement

You should prioritize using the colorless mana ability whenever your spells allow it to preserve your life total. Use the blue or black mana options only when necessary to hit specific color requirements or to stay on curve during the early turns of the game.

Interaction examples

Color Fixing in Multi-Color Decks

Command Tower

If you have both lands on the battlefield in a Dimir Commander deck, Command Tower provides either blue or black mana for free. If you need a second colored mana to cast a spell, you can tap Underground River for the specific color you lack, taking 1 damage to complete the casting cost.

Relying on Opponents

Exotic Orchard

If your opponent controls an Underground River and you control Exotic Orchard, your Orchard can now produce blue or black mana because those are colors a land an opponent controls 'could produce.' Note that your Exotic Orchard will not deal damage to you, even though the opponent's land would deal damage to them.