The translation you offer is a good one.
It should be noted, however, that translating short slogans correctly without context is often difficult or impossible.
Sometimes there is room for wildly different interpretations, but this one seems pretty clear.
The translation doesn't seem unnatural, but since it is out of context, the meaning may differ from the writer's intentions.
I would not call the translation "forced" without better knowledge of original context.
And even if there was a different original context, it does not rule out using the same phrase in a new context to mean something different.
Let me break down the sentence word by word:
- vi, "by the power". This is an instrumental ablative of the word "force" or "power" which unfortunately has no nominative (uninflected) form at all.
- veri, "of the truth". This is a genitive of the word verum, "the truth". This could also be the adjective "true", but it does not seem to refer to any word within the phrase. A less ambiguous word for truth would have been veritas, or veritatis in genitive.
- universum, "the universe". This appears to be the accusative object. Spelling the vowel 'u' with 'v' is not uncommon in Latin, and there are different views on choosing between the two letters.
- vivus, "alive". This is an appositive attribute to the implied subject ego, "I". This Latin structure does not have a clear English counterpart, so you have to translate it in a way that best fits the context. (In Finnish this is quite well captured by the essive case.) Something like "I, (while / due to / despite) being alive, …" is a bit heavy, so "I, mortal" sounds just right.
- vici, "I won" or "I conquered". This could also come from the word vicus, "village", but it makes most sense as a form of the verb vincere. This interpretation might change if the phrase was part of a longer one.
The word order of Latin is relatively free, and the one in this phrase feels natural.
The translation is of course slightly forced into having every word start with a 'v', but I guess that the whole phrase was coined so as to facilitate these initials.
Nevertheless, I cannot suggest a significantly more natural Latin translation of your phrase.
I would replace veri with veritatis, that's all.