An item being niche isn't a good reason to remove an item.
An item causing degenerate gameplay (see: DFG, Innervating Locket, ect) is a good reason to remove an item.
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Reduced AD, higher HP, and keeps its active that serves more or less the same purpose. Entropy really isn't worth building as an offensive option most of the time, but making it a better defensive option would certainly make it more attractive.
Remake/combine Mallet with Ionic Spark as an HP/OnHit/IAS item. Auto attacks build 1 Frost charge and skills build 2. At 8 charges your next basic attack consumes them and cause a freezing blast of ice to detonate on the target, dealing damage in an area and slowing the target for 2 seconds.