Against galio, Avoid grouping closely together in team fights as it may enable Galio to get a 5 man knock-up with his R once one of his allies has engaged. Space out between one another for maximum survivability from the get-go.
 
If Galio uses his Ultimate R when you’re near him, you can disrupt it with any crowd control abilities. This will be very helpful as it can stop him from using his Ultimate R to help his allies.
 
In team fights, try to harass and poke him down as much as possible before he can look to engage. By poking him down first, you’ll make it impossible for him to look for an engage with his E and W. Against galio, Avoid regrouping closely in team fighting as this can allow Galio to get a 5 man with his R once one of his allies has engaged. Space between each other for maximum survival from the go. If Galio uses his Ultimate R when you are close to him, you can disturb him with any crowd control capability. This will be very useful as it can prevent him from using his Ultimate R to help his allies.