@Riot QOL Heimer suggested changes.
He completely depends on turrets for damage, thats his deal, he pays for it having the worst mobility in the game, to the point that even if he had 
's Ult as a basic spell he would still have crap mobility.
Once the enemy realizes he can kill his turrets, he is done, unless he set's ahead he are going to have a bad time.
His problem is how easily he is countered by almost every champion with a ranged attack or ability, and how easy turrets (including ult-turret) is killed, specially in the mid-late game.
Suggestion:
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Have his turret receive reduced damage from **ranged ** attacks and abilities. This would make his turrets more defendable while not affecting how he interacts with pure melee champions.
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Have his turret's HP scale better with his AP into the mid-late game, or make the turret's HP scale with Heimer's HP
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Fix turret's AI (kinda as with Zyra's plants), i constantly see Heimer's turrets stop attacking a low HP champion to attack a full HP tank, sometimes they stop attacking all together and so on.
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Change one of his abilities to shield Heimer and his turrets (As a random example) : Replace E (grenade) with:
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- Passively grants N Armor and MR to turrets. Heimerdinger's turrets are shielded by X+(Y% AP) for Z seconds, after that, his turrets emit a shockwave that slow nearby enemies, if an enemy is hit by 2 or more shockwaves, he is stunned instead.
