Glacials need counterplay
Let me open by saying that I don't think glacials are super overpowered... This is not a post to "nerf" glacials. This is to simply point out that glacials, while not insanely overpowered... don't have any real counterplay. (On the chance that they were ever buffed in the future, it would be very easy for them to become extremely oppressive due to the lack of counterplay)
As title states... besides 6 yordles (just making them miss alltogether) there is really no counterplay to glacials. At first I thought maybe a smaller group bonus would be good counterplay (6 yordles just to combat a glacial team seems a little ridiculous and unbalanced). But then I remembered Rapid Fire Cannon and how that single item built in the right circumstances helped my ranger team destroy a yordle team that should've hardcore countered me. I remembered building a morellonomicon on my chogath to completely shut down a nobles team with the aoe healing debuff. I remembered building dragon's claw when I saw sorcerer teams getting out of hand. And I immediately knew what should be done... Just make an item with "tenacity" on it. I mean... real simple. An item is accessible to each and every player if they play their cards right and get a little luck. This allows for players to still feel like they have autonomy in their choice of team composition, while giving them the strategical choice to equip that select party composition with items to counter enemy compositions.
Honestly... I would change one of either the shrink or another attack speed item and replace it with the runaans hurricane. And then spatula and negatron cloak could make "Mercury Treads", which would give tenacity (amount obviously up for debate, but I was thinking similar to base game maybe just a 35-40% decrease) to allies in a line while also providing small magic defense buff for the user.
Balance wise this item could have some effect on certain characters like; Pyke, Lulu, Morgana, Poppy, Twisted Fate, Cho'gath, Sejuani, Yasuo, Kennen, and probably some others that didn't come to my head immediately. I don't think it would gut these characters though, I feel like they would still retain their usefulness, Sejuani and pyke might feel this item the most. But that said, it wouldn't be an overall useful item save for specific circumstances. If it used Negatron cloak and a spatula. There are tons of other useful combinations for each of those items. So it presents the player with a choice of if glacials are going to be enough of an issue to commit an item to it.
TL;DR: While not broken or overpowered. Glacials has no counterplay currently. I believe an item that provides tenacity would give that counterplay without completely breaking glacials.