BeastMasterGuan ALL MODES

In short, this is my first build/guide, simply because I am playing Guan Yu currently with this build. I apologize if it is low quality As such, any constructive criticism is greatly appreciated.

Essentially, this is an extremely unorthodox build that I honestly wouldn't take into ranked play. However, I've been using it in Joust and Siege rather effectively.

From my perspective, people don't see Guan Yu as a damage dealer outside of using Taolu Assault and rushing you down with Cavalry Charge. Using this build, you will certainly surprise the enemy team by shredding squishies with your basic attacks.
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Combos!
I suggest using Warrior's Will as your engage, following up with Taolu Assault (which you will want to cancel early, we're using it to steal Protections, you only need it to hit 3x), then demolishing their health with your 4-hit basic combo.

Hunters, Mages, and Assassins will melt under this sudden pressure that takes place in about 3-4 seconds. The reason I build Titan's Bane is so that this also does shocking damage to Protection heavy Warriors and Guardians. Speaking of Warriors and Guardians...

I prefer to box with the Warriors and Guardians a bit prior to fully engaging them with my abilities. This lets you gauge your opponent and see whether or not it's a fight you can win. If they melt your health faster than you can damage theirs by a significant amount, use Warrior's Will to dash away (preferably through them for the slow) and then use Conviction as a damage buffer.

Alternatively, if they do out damage you but not by much, tip the balance in your favor with Conviction for the buffer, followed by Taolu Assault to raise your Protections while lowering theirs, again, end this early and continue your basic attacks. When (not if) they begin retreating, use Cavalry Charge to chase them down, cancelling it early for the stun.

It is important to pick up a mana buff early game to avoid backing as long as possible, in the late game, your mana count is usually high enough to sustain yourself and your team without it.

Early Game: Go in ahead of your team and flurry with Taolu Assault, and be prepared to turn around and use Warrior's Will to escape to your team, throwing down Conviction when surrounded by friends, using Meditation as necessary and available.

Late Game: Go in hard with Warrior's Will, initiating teamfights at the edge of your blade. Follow with a whirlwind of steel with Taolu Assault, building stacks on your passive. Heal your teammates, rinse and repeat. At this point your cooldown will be 3 to 4 seconds on your heal, so you'll be able to stay alive indefinitely as long as you keep away from supremely high burst damage.