As Terran
Make:
Marine
Thor
RavenVikings are fragile when forced to land or fight unsupported.
Open in the counter tool with Viking tagged ->As Protoss
Make:
Stalker
Phoenix
High TemplarFeedback and Blink punish Vikings that drift ahead.
Open in the counter tool with Viking tagged ->As Zerg
Make:
Hydralisk
Corruptor
InfestorFungal makes Viking retreats unreliable.
Open in the counter tool with Viking tagged ->
Marauder
Reaper
Hellion
Hellbat
Widow Mine
Cyclone
Siege Tank
Medivac