Looking for a name of my account in an MMO. The game mode I have selected for the character is that you can only die once, so I wanted to get a bit clever with the name. So, how do you say "One Death" in Latin? Google says "Qui Mortem" but I wanted to double-check.
The most straightforward way to say "one death" in Latin is mors una. If you like it better, you can also swap the order to una mors. If you want to be playful (as I gather you might), the spelling the two words together as Morsuna makes a natural-sounding name and leaves the Latin less obvious. This spelling is not valid Latin, but maybe worth consideration in the context you have.
The suggested translation qui mortem is unfortunately nonsensical. On its own it's hard to translate to English, but if we add, say, the words is ("he") and timet ("is afraid"), we get is qui mortem timet, "he who is afraid of death". Perhaps the best literal translation is "who death", but it doesn't quite capture the Latin.
Suggestion regarding Google Translate and Latin: Instead of double checking what it gives, ignore entirely what it gives. It's horrible. Instead, it's better to use an online Latin dictionary — even if you don't really know what to do with the words. And, better yet, ask someone who knows Latin. This site is a good choice.