Underground Mortuary is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

(: Add or .) This land enters tapped. When this land enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Complete guide

Underground Mortuary is a powerful utility land that bridges the gap between mana fixing and deck manipulation. As a dual land with the Swamp and Forest subtypes, it provides essential color support while allowing you to curate your next draw.

What Underground Mortuary Does

Underground Mortuary provides both Black and Green mana, making it a staple for Golgari-themed decks. It has the Swamp and Forest subtypes, which means it can be searched for by effects that look for those specific land types. When it enters the battlefield, you perform a Surveil 1, looking at the top card of your library and deciding whether to keep it there or put it into your graveyard.

Step-by-Step Resolution

First, Underground Mortuary enters the battlefield tapped; you cannot use it for mana the turn it is played unless an effect untaps it. Second, its triggered ability goes on the stack. When this ability resolves, you look at the top card of your library. You then choose to either leave it on top or move it to your graveyard, which is excellent for setting up graveyard synergies or ensuring your next draw is useful.

Common Mistakes to Avoid

A common mistake is forgetting that this land possesses basic land types without being a basic land itself. While you can fetch it with cards that search for a Swamp or Forest, it does not count as a 'Basic Land.' Additionally, the surveil ability is a triggered ability that happens upon entry; if an effect prevents enters-the-battlefield abilities from triggering, you will not get to look at your top card.

When to Play It

You should play Underground Mortuary early in the game to fix your mana colors or later in the game when you need to dig for a specific answer. Because it enters tapped, it is often best played on a turn where you do not need to use all your mana immediately, allowing the surveil trigger to help you plan your subsequent turns.

Interaction examples

Mana Fixing Strategy

Command Tower

If you have Underground Mortuary and Command Tower on the field, you have reliable access to Black and Green mana. While Command Tower provides immediate mana, playing Underground Mortuary first helps you filter your deck for a third color or a key spell.

Optimizing Your Draws

Exotic Orchard

When playing against an opponent with Exotic Orchard, your Underground Mortuary provides them the ability to produce Black or Green mana. On your end, playing the Mortuary first allows you to surveil, ensuring that your next land drop or play is exactly what you need to stay ahead of your opponent's mana production.

Guide written with AI from the official text and rulings. Official English text prevails.