The BEST ways to refresh bair is by pummeling after grabs... With our deceptive grab range and our good shieldgrab, running past a spacing enemy, shielding (or powershielding), and grabbing them will get you a couple of easy pummels, plus a dthrow and maybe a follow-up or two (like dthrow>bair, bthrow>bair, bthrow>uair...)... You keep your game up like that, refreshing your bair with our lightning-fast pummels (the mashing of a button is innate to an MK main, and we are all innate MK mains, so mashing the 'A' button will be easy) and getting free damage with throws, and you'll have your bair fresh whenever you need it fresh! :D