What would the name and formula be for Mo+O+Se?
Well, molybdenum oxysulfide is apparently a real compound with the formula $\ce{MoOS2}$ or $\ce{MoO2S}$.  Since selenium is a chalcogen and has (some) chemistry that is analogous to sulfur, I think molybdenum oxyselenide would be an appropriate choice.

More formally:


Molybdenum(IV) oxide is a compound with the formula $\ce{MoO2}$.  
Molybdenum(IV) selenide, also called molybdenum diselenide, has a formula of $\ce{MoSe2}$
Molybdenum sulfide selenide exists and has the approximate formula $\ce{MoSSe}$.


Thus, perhaps molybdenum(IV) oxide selenide would be another choice.