His waveclear and burst damage is impeccable. He can also keep poking the opposition with his W and set some Q turrets in the lane brushes/around him to prevent all-ins.
He can push up freely as long as he is in the cover of his Q turrets. These turrets, when combined with his E, can allow Heimerdinger to turn an enemy gank into an easy kill for him.
His Ultimate R provides him with a lot of versatility. He can use his empowered Q to take down turrets and enemies, his empowered W to take down low health enemies, and his empowered E to set a multi-man, long-ranged CC which can allow his team to follow up on his CC.
If the enemy team focuses on destroying his Q turrets before all-in’ing him, he will have to play defensively till he can bring his turrets back up.
Missing his E will put him in a vulnerable spot, especially if he is laning on his own or when he is pushed up. This mistake can easily get him killed.
He is very effective when he is fighting in closed spaces like the Jungle. The enemy can reduce this by fighting in the lanes and then matching his push if he tries to split push. Even in this case, if the enemy destroys his Q turrets, Heimerdinger will be done for.
0 - 15 min
Focus on farming in the early game. You need to earn as much gold as possible to be a major threat later on.
You’re going to naturally push the minion wave with your Turrets Q. While you’re pushing, keep a constant eye on the map. Heimer is vulnerable to ganks if he doesn’t have 3 Turrets Q up, so keep this in mind.
If the enemy laner roams, don’t bother trying to contest their roam. Instead, push the minion wave and start earning turret plate gold.
15 - 25 min
Split push and draw aggro while your team applies pressure elsewhere on the map.
In team fights, use your empowered E to get picks to start the fight. Catching someone out and subsequently getting a kill could provide your team with enough time to take the Baron or Dragon.
Peel for your team in team fights. Use your Q on the nearest champion to protect yourself and your ADC.
Heimerdinger can take objectives really fast in the late game thanks to his Turrets Q. Be prepared to make the call for them as you can often cheese them for free.
Look for picks with your E to start the fight. If you’re able to CC the whole enemy team, you will give your team a good chance of winning the game.
Continue to peel for your allies to keep them alive in fights. You’re good at peeling, so you should do so in the late game.
level 3 is a decent powerspike as Heimerdinger will have access to all his abilities. He can easily CC immobile ADC and burst them down with his turrets and rockets. His E will be very beneficial when going for objective fights.
Level 6 is arguably a colossal power spike for Heimerdinger, as he can now bait enemies to their deaths with ease. He can also take towers very quickly or slow multiple enemies with his E.
The first mythic item will allow Heimerdinger to dish out a ton of poke damage in the lane with his turrets. His burst damage will be pretty potent as well, and he can one-shot enemies with utmost ease.
Level nine is a massive powerspike for Heimerdinger. He will now have maxed out an ability and will be dishing out a lot of damage depending on his maxed ability. Additionally, as a mid laner, he will now be able to CC and blow enemies up with his abilities.
Adding another point to his Ultimate R will skyrocket his overall power in the lane. This is because the empowerments will be more powerful, and Heimerdinger will use them both offensively and defensively. In addition, it will let him harass the enemy laner relentlessly when they are trying to farm in the lane.
Heimerdinger excels during team fights as he can control a large area with his Q turrets. This will be really useful in clumped areas like the objective pits and the Jungle paths.
His E allows him to CC key targets but has a long cooldown early on. Fortunately, he will not have this problem during the late game and will now take down many enemies with his E.
Adding another point to his Ultimate R will give his empowerments more overall strength. It can be convenient when taking neutral objectives and fighting enemies who rely on diving and locking Heimerdinger down.
Heimerdinger will have many items now, and his abilities can easily one-shot enemies if they are not careful or if Heimerdinger sets a death brush somewhere. He can also take on the Baron singlehandedly.