You continue to provide top notch QC / feedback, and we appreciate it.
While nejimakipiyo is the main translator, Mortamor/Deathmore's name choice was the result of a lengthy discussion between us. Deathtamore is the transliterated English rendering of the katakana name in Japanese. When it comes to the English katakana words that are used in Japan, sometimes they are the most common word for something, other times they are a secondary, exotic kind of word. Such is the case with "Death" here, where "Shin" is the common Japanese word for death, and English "Death" is the exotic one. Therefore, if we represented it as "Death" in English, we would be swapping an exotic word for a common one. In the effort to provide like for like equivalency in these kinds of situations, we have frequently looked to Latin or French words as a substitute for the katakana English word. They are more exotic, being derived from another language, yet still convey a clear meaning for the bulk of the audience. In this case, we felt that the contemporary official localizers had made a good choice in Mortamor, with "Mort" / "Mortem" being the Latin derived word for death.
We encountered a very similar situation with the DQ4 boss name. Death Pisarro is the Japanese name, with the same English katakana word being used for Death. The original loc named him Necrosaro. We were impressed by their exotic word choice with "Necro", but we didn't like his proper name Pisarro being chopped, nor did we like how clunky Necropisarro would sound. The contemporary official localization's choice, Psaro the Manslayer, sounds nice, but takes too many liberties for our stomach. After revisiting the conversation several times over the course of two years, we eventually decided on Pisarro Mortis. It preserves the name Pisarro, and "Mortis" works as an equivalently exotic rendering of "Death". We also think it sounds pretty cool.