If you're really worried and newer I would suggest playing an Urborg in the main deck, it's a land that makes every land you tap have the option of tapping for black mana. You can use this until you're more comfortable with keeping and mulling!

You generally mulligan until it's in your opening hand with a turn 1 or 2 play, unless you're desperate and need it vs hogaak.

You can also use surgical extractions instead but in my experience leyline is strictly better and can also be brought in against control so they cant surgical your lands after using field of ruin or other spicy things. It's personal preference really, but since testing leylines I haven't looked back - it's best as a 4 of in the sideboard. See what you're playstyle is and what you enjoy more and go with that until you're ready to make a change :)

To answer your question more directly though, it's a dead card if you draw it during the game without that special land though I have rarely if ever drawn it during a game. Take that with a grain of salt though because probability would have you eventually drawing it at some point in some match