Stalltwo should use Psystrike as an attacking move over one of the screens, as it's still pretty powerful even without investment.
Edited that in, on to the counter.
Ho-Oh @ Leftovers
EVs: 192 HP / 216 Atk / 24 Spe / 76 SDef
Adamant Nature (+Atk, -SAtk)
- Light Screen / Brave Bird
- Sacred Fire
OK so this is a really large alteration of Sub-Ho-oh, better suited to take on threatening Special Attackers. If Ghostceus is using Roar, it can spam Sacred Fire on it till its burned, and then have some special attacker remove it from play. If its using Calm Mind, it gets phazed by Ho-oh's Whirlwind and its attacks tickle after a Light Screen. Focus Miss being used really does neither lol so it doesn't fear much :D and can just burn the thing (or pp stall).
This thing also has the unique niche of acting like a Special tank on sun teams, capable of shoving off Draco Meteors before Stealth Rocks are up and then proceeding to retaliate with a Sacred Fire, Brave Bird, or just Roost. Also counters Darkrai as even a +4 Dark Pulse fails to OHKO while it OHKOes in return with a Sacred Fire.