GLP has no cast time anymore.
Over all of the item changes, one of the most impactful is the removal of GLP's cast time. This creates a myriad of situations and builds that previous patches cannot achieve.
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Glacial augment midlane/jungle. It can now be used aggressively as a ambush tool. I personally like this change. One of the most scary stuff you can pull off with this combo is with Eve. You literally have the functionality of your old ult back. Play your cards right and you can be a massive peeler, catcher.
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Builds for burst mages. Now leblanc doesn't need to build gunblade. That extra ad is no more needed.
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Fast combos. Fluid motion. One of the giant reasons this item failed was the need to stop in your tracks to fire it. You were not able to use it in combos, or chase the enemy with it.
, which is something you almost never need on anything but top or mid laners, and even then GLP was contested stat wise for 
etc may appreciate GLP, but they need the electrocute damage in order to burst their target way more then the slow, and the item will be enough on its own to help them as much as protobelt would. (if its better then proto)