Few pokémon have suffered such indignities as Beheeyem. Sure, its normal to be completely outclassed by another pokémon that does everything you do but better. But to have it happen in the same generation that you were introduced?! Beheeyem has long labored in Reuniclus's shadow. Despite Reuniclus only having a mere 5 BST over Beheeyem, its stats are much more optimized (taking a hit in Attack, Speed, and Special Defense for much better HP), in addition to far superior abilities (Overcoat, Magic Guard and Regenerator vs Analytic, Telepathy and Syncronize). And Reuniclus wasn't even Beheeyem's only competition. Musharna also fills many of the same roles as Beheeyem and Reuniclus.
Oh wait, what about Doubles you say? Surely Telepathy gives Beheeyem a niche there. Again outclassed by Reuniclus, whose far superior bulk makes it a much more reliable Trick Room setter.
Truly the most interesting thing about Beheeyem is its persistent ability to Learn Steel Wing despite its lack of wings.
Admittedly, the generation shift was kind to Beheeyem, giving it Teleport and removing Pursuit (though the strengthening of Knock Off was not welcome), which thanks to its average bulk and access to Teleport enables Beheeyem to act as a reliable pivot, able to Safely bring checks and counters in repeatedly thanks to Recover. But really, just use Reuniclus instead.