Garen has always had power. With max cooldown and lots of health, he is not only a powerful health tank, but possibly one of the best champions. At 450, he is worth the cost. However, his health potential is best drawn out by Warmog's Armor. In ARAM, on Howling Abyss, Warmog's Armor is unavailable. But even with it out of the picture, his damage potential and tankiness need not be affected.

The two builds are a damage tank role (build 1) and a support tank role (build 2). Use is based on judgement, but a summary of each is explained in the Items category.

The runes I choose are my jungle runes on most occasion. This means Greater Seals of Armor and Greater Glyphs of Magic Resist, to tank early. The Greater Quintessence of Movement Speed allows you to get in and out of combat fluidly, to protect many an ally. The last spot I filled with Greater Marks of Attack Speed. This allows some damage to stack. Early, it seems less useful, but once Black Cleaver is built, it stacks the passive quickly. Even without, every attack added is more damage dealt, and speeding that up is always worth it.

This one was a hard choice. Flash is a must on any map due to its sheer usefulness, but in ARAM, the other spell can be many. Some that seem otherwise useless, like Heal and Clarity, can be surprisingly useful. Other good spells, like Ignite and Exhaust, still make useful tools. But above all, since Garen's purpose is to tank, I took Barrier. It helps to tank much faster, and at later levels, proves to be invaluable for turret diving.

That said, Heal is a better choice for a team of all squishy champs other than you. This will actually help to keep them alive longer in the end. That has, and should always be, your primary goal. Teamwork is the key in ARAM, and in every mode. Remember to put your team first, ALWAYS.

In ARAM, since you start at level 3, it is usually better to start with one of each skill. The same goes here. After the start, it's better to rank up your Judgment. Since champions tend to cluster together, this useful spin can damage all five enemies it used right, and even if used incorrectly, it tends to discourage others from entering the fray. If one is isolated, they tend to die faster, and gives the advantage to your team.

After focusing Judgment, Decisive Strike is the next ability to focus. It speeds you up and adds damage. You can drop the stragglers and the ones that try to run. It can also rush in, initiating combat as well. Courage gives enough bonus at even rank 1, so it doesn't need the extra ranks.

Only Demacian Justice overrides this, at levels 6, 11, and 16.

As you can clearly see, there are 2 builds listed. The first build is a tad more armor oriented, and is designed to pierce multiple tanks while tanking. This is usually the safer build, and is made to be reliant more on yourself, for damage and tanking. The problem with this build is twofold: though it wrecks tanks easier, AP champs deal a bit more damage. In addition, this build lacks solid life gain. This means either you need a support that can heal, or you may need to rely on your passive.

The other build is a tad more reliable, but also far less damaging. Tanks can easily armor up so that you dish out little damage. Though you dish out less damage, you are far harder to knock down. Additional MR makes AP useless, and the shield from Maw of Malmortius makes it even harder for AP champions to deal any damage. The high armor stops AD, and the lifesteal keeps you going. Normally 10% doesn't help, but thanks to Spirit Visage, it doubles for you. It also helps any ADC keep their life up as well, which is always good.

The builds aren't that different, but always rush the cooldown items first. For build one that is Black Cleaver and Locket of the Iron Solari and for build two it is zeke's herald.

With two possible builds, you can tank greatly, being an unstoppable wall to protect your allies. Be it a high damage build or a more support role, Garen is a unstoppable force. And though you may not be familiar with him, since you got him randomly, you can always help your team in securing a victory.

Thanks to jhoijhoi, for teaching me code.
Thanks to Maintained, for showing me jhoijhoi's guide.
And thanks to you, for reading this.

Good luck, and may the bacon be with you.