Against cassiopeia, In team fights, do not group closely together to make it impossible for her to land a 5 person Ultimate R. Be prepared to turn around if she looks like she’s about to cast her Ultimate R.

Never fight the enemy in the jungle or around an objective as her Ultimate R is really good in tight areas when teams are clumped together. Fight spaced out in a lane when possible. 

Cassiopeia will look to ambush or assassinate targets that are moving through the river alone. Unless you know where Cassiopeia is, do not walk through the river or around the map on your own especially if you’re squishy. If you die, she may cost your team the next team fight or objective. Against cassiopeia, In team fights, don't regroup closely to make it impossible to land a Ultimate R. Be ready to turn if she looks like she's about to launch her Ultimate R. Never fight the enemy in the jungle or around a goal like her Ultimate R is really good in tight areas when teams are stuck together. Fight spaced in a track when possible. Cassiopeia will seek to ambuish or assassinate targets that move across the river alone. Unless you know where Cassiopeia is, don't walk across the river or around the map on your own, especially if you are squishy. If you die, it could cost your team the next team fight or goal.