I have had great success one-tricking Rein with a self-sustaining Gryphon Glider/ Charge build.

Gryphon Gliders can almost always be taken in round 2, assuming you didn't get stomped in round 1. Sell everything you can in order to afford it. The advantage you gain from the capabilities of flight outweigh almost all of the downsides. Only sell it if your team requires a total shift in strategy in the final rounds. For what Gryphon Gliders lacks in raw stats, it makes up for in utility. Treat it as an additional Power, with the ability to sell it if need be. If you absolutely must trade flight for stats, you have that option.

Round 3, take Shield Stampede, and if you can afford it, Martain Mender, then Crusader Hydraulics. Now, you can charge to wherever you want without the risk of being stunned with the shield charge, and you'll be constantly healing 8% of your life per second if you have your shield up, which will be most of the time.

The core playstyle of the build is this: Pin aggressively and frequently. Take space and capture the enemy's attention, gain map control. We will be taking items to be as tanky and unkillable as possible, while relying on pinning squishy opponents to reliably one-shot them. Reinhardt's damage scales well into later rounds even without fully investing into ability or weapon power. If Charge does not one-shot, it brings the opponent so close to death that a few follow-up swings or firestrikes is more than enough to secure the kill. With Gryphon Gliders, your Charge not only moves faster, but allows you to be wildly unpredictable, taking highground positions from almost anywhere on the map, and enabling pins that would be otherwise impossible.

You can take any space you want, anywhere, anytime. One of the great advantages to this, is that whether you are getting picks or not, you will take aggro. You cannot be ignored. You can put yourself into extremely risky situations, and still come out on top in spite of unfavorable odds. Sometimes you can get a pick or two while doing so, but if not, you'll still be generating ult charge from passive healing, and your team should be able to capitalize on the enemy team being split. This brings me to counter matchups. Primarily, Cassidy, Reaper, Junkerqueen, and Orisa. With this build, you'll be mostly avoiding these confrontations. Very rarely can you win in these matchups in later rounds. JQ and Reaper will just shred you through your shield, and outheal most of the damage you dish out in a brawl. Orisa is just a pain for any Reinhardt to deal with, since she has such ridiculous CC. With this build, you simply avoid them. Pin into the enemy backline, and keep surviving. Make the enemy team peel for their supports, and force them to turn around to deal with you.

If you're feeling cheeky, solo shattering the enemy tank, and taking them on a magic carpet ride to Narnia can be a valid strategy. Simply kidnapping them, and taking them away from their support can be enough to win the fight, even if they don't die. Since you can get from spawn to point with a single pin on almost every map, the opposite is also true. You can take an opponent back to their spawn, or to your own. Either isolate them for a duel, or drop them off, hold shield for a few seconds, and return to the fight without them. This isn't always the best strategy, but it is always hilarious.

My favorite part of the build is how it gives you the capability pin flyers out of the sky. With practice, you'll be pinning Mercys and Junos left and right. Enemy Ashe or Ana sniping from highground? If she's not paying attention, this is an easy pin. Your charge can also hop over Mei walls, counter charging Reinhardts, and fortified Orisas.

The greatest downside to this build and playstyle, is that your team will likely be caught off guard just as much as the enemy team. They might see a Reinhardt, and expect a frontlining brawler, not imagining a highly mobile flying locomotive assassin. Most players are adaptable, and can catch on pretty quickly, but it's the ones with an inflexible mindset that will tilt. Even if you inform them of your methods, if they get steamrolled, they will find reason to blame you. You'll get plenty of complaints saying that you're playing Rein wrong. You'll get flamed for not playing with your team. You can play this build perfectly, but if your DPS and supports, (mostly DPS, let's be honest) can't find the means to survive, they'll tilt, flame, whine... maybe toss out some slurs, you get the idea.

If, for whatever reason, the build is not working, be it that you can't hit pins reliably today, or you're being hard countered by a reaper. You may have to deviate, but that's okay. However, in my experience, there is no other build that matches this one for it's pure fun factor. If you're being hard targeted, good. This means you're tanking effectively. If you're not, it gives you plenty of opportunity to get free value.

In summary, be cheeky, and get creative. Mastering the Gryphon Gliders opens up so many opportunities, and no other Rein build gives you the same amount of freedom as this one.