In case you weren't playing Magic back in Theros block, at its core, Bestow is a mechanic that turns a creature into an Aura enchantment when cast for an alternate cost, otherwise known as the bestow cost
Again, its a great way to get a decent amount of packs, with a nice box to store and sort your decks and spares
But you could also take a more aggressive route and use this commander to copy combat tricks and even auraswhich falls outside the traditional definition of spellslinger, which seems to keep shifting as Wizards prints more cards that broadly care about noncreature spells
Thanks to how many mill cards are available, the hurdle of milling about 90 cards isn't too extreme
Seek out a Legendary Creature that has a simple and effective gameplan and use it to your advantage.
If an activation cost is, though, you'd still have to pay