As per the title, I am looking for how you you would say 'Spirit Subjugator' or 'Soul Enslaver' or something similar.
For "soul", you have a couple options. One of these is spīritus. Quoting Tom Cotton's answer to another question:
Spiritus was more tangible, the very ‘breath of life’, the actual ‘life force’, or ‘life principle’. It became symbolic of the spirit by which men might feel themselves driven, and thus the ‘mental spirit’ related to ardour and courage. It was later used for ‘spirit’, ‘soul’ or ‘mind’, and was close in meaning to mens, the active faculty of recollection, intellect and understanding.
In Christianity in particular, the Holy Spirit is the spīritus sanctus, and when Jesus died he ēmīsit spīritum. In the Vulgate, it generally corresponds to Greek pneuma, Hebrew ruahh, English "spirit".
Another option is animus. I don't have as poetic an explanation for it as Tom, but the animus is what humans have that animals don't: sentience, consciousness, the rational mind, however you want to put it. It's notably not quite the same as mens, "mind", since mens atque animus "mind and heart" was a common idiom (like English "mind, body, and soul").
In Christianity, this is the usual term for a "soul", as in "the part of a person that isn't the body". In the Vulgate, it generally corresponds to Greek psychē, Hebrew nephesh, English "soul".
For "enslaver" or "subjugator" you also have a few options.
Most literally, the person who sells slaves to people is an addictor, with someone who had been legally enslaved (usually for a debt) being addictus rather than servus.
A more explicit verb is sub-jugō, "to put under the yoke (jugum)". So a subjugator might be, quite straightforwardly, subjugātor. This has a sense of conquering a new territory and selling its people into slavery, rather than just overseeing an auction: it's what Caesar did to Gaul.
Grammatically, you'll probably want "subjugator" in the nominative, and "soul" in the genitive plural: subjugātor or addictor, and spīrituum or animōrum. Literally, "the subjugator of souls".
Subiunctor Animorum, perhaps? Subiunctor Spirituum?
These are fairly literal translations.