The Arcane Ward summoned by Medivh’s Unstable Runes equipment does not Counter every ability, below is a list of the abilities the Arcane Ward ignores.
Beastly Beauty - Genn Greymane
Beautiful Beast - Genn Greymane
Dragonmaw Poacher - Gruul
Fel Infernal - Lord Jaraxxus
Tentacle of C’thun - C’thun
Devilsaur - King Krush
Nightmare Viper - Lady Anacondra
Pufferfisher - Murky
Felfin Navigator - Old Murk-Eye
Giantfin - Old Murk-Eye
Hulking Overfiend - Rathorian
Bladehand Berserker - Varok Saurfang
Evasive Wyrm - War Master Voone
Spirit Guide - Drek’Thar
Water Elemental - Jaina Proudmoore
Spawn of N’Zoth - N’Zoth
Void Consumer - Tamsin Roame
Wavethrasher - Zar’jira, the Sea Witch