Ice, more Ice, Psychic, dragon resistance, - it looks like a job for Jirachi. It is faster than the therian forms and as fast as Salamence, resists dragon and has way more HP than Genesect.
The Scarf one (252/252) is similar to Genesect, a bit weaker, but funtions well enough. It has enough power to OHKO Mence with Ice Punch. It struggles a bit against Gliscor though so be prepared to U-Turn a lot, unless you are Adamant. Iron Head is suggested, but if you are willing to take a loss in accuracy, Zen Headbutt checks both Terrakion and Keldeo at the cost of Kyurem-B (they rarely come in anyway, because they expect Iron Head).
Otherwise, a bulky Water like Jellicent can check these apart from Thundurus-T, for which you hopefully have Gastrodon alive. Ferrothorn too, just watch out for Landorus and Keldeo.