Here's a link to the wiki that has both the item's description as well as an explanation of what it actually does. The bonus magic damage is only applied once per target, but the description doesn't mention that at all. It makes it sound like it's good for sustained dps, but it actually only synergizes with high single hit damage like jhin's 4th shot/caitlyn's headshot/trinity force users/etc. I think the description of the item should be updated to reflect what it actually does, since most people who have only read the in-game description and not the wiki probably misunderstand it.
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