Much Needed Garen Update / Mini Rework
It has been some time since Riot has enhanced Garen's kit, especially after staing in 7.14 that his buffs were the "start of a larger discussion" concerning Garen.
His early game needs a little enhancement, but the major section that needs improvement is his teamfighting relevance. What Garen lacks in a teamfight is initiation; therefore, if he has no clear method of doing so, he needs to be able to simply reach the enemy backline. Period. Also, when he gets there, he needs to be able to provide meaningful impact to the teamfight as it is occurring, as well as be able to survive long enough for his teammates to assist him.
These enhancements are meant to provide such avenues for him. At the same time, these suggestions are also meant to be realistics when concerned with what will Riot most likely be able (& willing) to implement into a champion like Garen. I have thought of more outrageous ideas that would be really cool to see on him, but would make him broken and make playing him (& against him) less competitive or fun. With that in mind, let's dive into it.

Passive - Perseverance (Make early levels stronger)
"Vile scourge": From levels 1-10, taking damage puts Perseverance on an 8 second CD instead of 9, & his regeneration increases to 4% when he is below 50% health instead of 25%.
Q - Decisive Strike (Without clear engage, makes movement more functional in game)
"I Will Lead the Charge": At level 11 & after, Garen's Q now also grants slow immunity for the duration (1.5/2.0/2.5/3.0/3.5 seconds).
"Charge!": Garen receives 30-60% increased movement speed (based on champion level) when activated.
Really Decisive: Garen's Q animation is now a complete auto attack reset (instantly triggering another auto attack).
"The scoundrels will pay!": Garen's silence against an enemy champion also disarms them, preventing them from basic attacking for the duration (1.5 seconds).
W - Courage (Extended combat survival)
Additional Passive - "Show Them the Strength of Demacia!": Garen's thrill for combat enhances his durability whenever enemies are around, granting him 6% bonus tenacity for each nearby enemy champion (up to 30% total bonus tenacity).
"I will fight as long as I stand!": While on CD, each instance of taking damage that would put Perseverance on CD reduces the CD on his W by 1 second.
E - Judgment (More teamfight potential than just armor shred & in-combat sustain)
"Justice, by law, or by sword": Enemy champions hit 4 times have their armor reduced by 25% & have grievous wounds applied to them for 6 seconds (hits after the 4th refresh the duration).
"Battle the Infamy": Garen reinvigorates his conviction through combat, healing for 25% of the damage dealt by his Judgment against enemy champions & epic monsters.
R - Demacian Justice (More impactful True Villain mechanic & better execute)
Passive - The True Villain: Garen marks the enemy champion with the most kills (changed from highest killing spree) as the Villain, causing his basic attacks and each spin of Judgment against them to deal 1/2/3% (increases with skill point level) of the target's maximum health as bonus true damage.
Active - "Victory Awaits": Garen calls upon the might of Demacia to attempt to execute an enemy champion. After a brief channel, he deals 175/350/525 true damage (not magic) plus 30/35/40% (slightly increased damage) of the target's missing health.
Please let me know what you think, thanks. :)

P.S. - As a side note, Garen should be a scary champion; when enemies are far away from him, they are safe, but if they are close by, they should legitimately be concerned about facing death very quickly. These enhancements should provide players the feeling that Garen IS relevant in any game is he played, and that whether you like him or not, you respect the potential threat he can represent.
When it comes down to it, Garen IS a simple champion. He is not very mechanically difficult to master, nor is he difficult to play as or against. It comes down to knowing general game mechanics and being comfortable with item builds and individual champion skills in order to play effectively (or not). these suggestions are not intended to make Garen an advanced champion - they are meant to enhance his simplicity to make it functional against all levels of play.
