It appears that you're asking 2 different questions:
1) Making human images/figures
(as adapted from @DonielF's stellar answer to: "Are Totem Poles considered to be Avodah Zarah?")
A: Humans
Shulchan Aruch, Yoreh Deah 141:4:
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אסור לצייר [...] וכן צורת אדם לבדו כל אלו אסור לעשותם אפילו הם לנוי ואם עובד כוכבים עשאם לו אסור להשהותם: הגה ומיהו אם מוצא אותם מותרים מלבד בחמה ולבנה שדרך העובד כוכבים לעבדם או שיש הוכחה שעשאן לעבדם שאז אסור ככל הצלמים כמו שנתבאר בריש הסימן: במה דברים אמורים בבולטת אבל בשוקעת כאותם שאורגים בבגד ושמציירים בכותל בסמנין מותר לעשותם
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It is forbidden to depict [... various images that are irrelevant to the topic at hand], and likewise the face of a human alone: it is forbidden to make any of these, even for decoration. If a non-Jew made them for him, it is forbidden to keep them. (Rema: However, if he found them, they are permitted, except for a sun or moon, as it's normal for an idolater to worship them, or anything for which there is an indication that they were worshipped, as then it's forbidden, like all figures, as was explained earlier.) When are these words said? When they are protruding [from the background], but when they are sunk [into the background], like those woven into clothing or depicted on a wall, with signs, it is permitted to make them.
Take a look at 141:7 which while granting leeway overall, may be in an issue in your particular case (since it's constructing an entire body):
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יש מי שאומר שלא אסרו בצורת אדם ודרקון אלא דוקא בצורה שלימה בכל איבריה אבל צורת ראש או גוף בלא ראש אין בה שום איסור לא במוצאו ולא בעושה
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There are those who say that the figure of a man or dragon are only forbidden when it's a full picture, with all of its limbs. But there is no prohibition at all on a depiction of the head, or the body without the head, not in finding it, nor in making it.
2) Avodah Zarah in video games
A further commandment prohibits looking at and thinking about idols. “Do not turn to the idols” (Lev. 19:4) is seen as a wide-ranging rule against studying idolatrous culture and literature (Mishneh Torah, ad loc., 2:1-2). This rule against learning about idolatry should forbid virtually worshipping the idol, as well. In playing the game, you are watching the idolatrous service as it happens, even though you are not technically participating in it.
Authorities are divided whether this prohibition applies to all idolatrous or only those that are no longer worshipped. In response to a question whether a teacher may cover Greek mythology in class, Rav Moshe Feinstein (Iggeros Moshe, Yoreh De’ah 2:53) rejects the suggestion that because no one currently worships the ancient religion, the prohibition no longer applies to it. Instead, he offers permission from another angle, that the education should be from the perspective of debunking the false stories. Otherwise, according to Rav Moshe, studying or watching ancient idolatrous religions remains forbidden.
I recall hearing in the name of Rav Joseph B. Soloveitchik that he permitted studying Greek mythology for the reason Rav Moshe rejected, although I never confirmed this. Even if he did not, we can find others who suggest it. Rav Yair Chaim Bacharach (Chavos Yair, no. 1 secs. 11-12 sv. ve-adayin tzl”a) suggests that the prohibition to say the name of an idol only applies to an idol that is currently worshipped. We may freely say the names of ancient idols. Darkhei Teshuvah (147:4) quotes a responsum of the Beis Yitzchak 1:YD:152) that agrees in principle with the Chavos Yair but is concerned that maybe someone in the world still worships the Greek pantheon. Because of this possibility, he refuses to consider Greek mythology an abandoned religion.
Some contemporary rabbis in Israel seem to follow the Chavos Yair‘a approach. Rav Shlomo Aviner (She’eilas Shlomo 4:167; Piskei Shlomo, vol. 2 p. 45) begrudgingly permits the study of Greek mythology. He cautions that it is full of nonsense and is a waste of time. However, he allows for leniency if necessary because the idolatry has been long abandoned. Similarly, Rav Yehuda Henkin (Bnei Banim 3:35:2) writes that if the religion is abandoned, the gods are no longer considered idols.
In this game, the idolatry is completely fictional. Not only does no one currently worship it, no one ever worshipped it. I believe that even Rav Moshe would not apply the prohibition to this religion because it is not, and has never been, a religion. It is simply fantasy.
