STOP! Hammer time!
Goal: Add Entropy to Summoner's Rift and give it a niche unique from Frozen Mallet via remakes. Return Ionic Spark to existence as a component of Mallet to give it a better build-up.
-Entropy is added to the Rift and remade. It now builds out of Phage, Pickaxe, and Brutalizer but it loses its active and gains a new passive. UNIQUE passive: Your single target spells and basic attacks steal 20% of the target's movespeed (15% for ranged) for two seconds.
Nice new passive, good buildup, great item for sticking to targets, alternative to Trinity Force for folks that want more attack damage.
-Ionic Spark returns! It builds out of a Recurve Bow and a Ruby Crystal. It grants attack speed, HP, and some OnHit magic damage in addition to the following. UNIQUE passive Stormblast: Your basic attacks build charges. At four charges your next basic attack (onhit) consumes the charges releases a chain-lightning that deals 100 magic damage to up to 4 enemy units.
-Frozen Mallet's build is changed to Ionic Spark and Giant's Belt. It grants MOAR HP, a little more attack speed, some OnHit magic damage, and an augmented passive. UNIQUE passive Stormblast: Your basic attacks build charges. At four charges your next basic attack (onhit) consumes the charges and blasts all foes in an area with an icy explosion, slowing them by 40% for 1.5 seconds, dealing 100 magic damage, and applying OnHit effects to all units hit.
Just to be clear, your primary target doesn't get hit twice by OnHit effects. That would be a little bit absurd on a few champions who will remain unnamed.