Items:
14.8 has nothing major in terms of items but QSS will no longer be useful against Mordekaiser, making it an item never to be built on Rell for any situation as of now once 14.8 hits

Rell Related Buffs/Nerfs:
Nothing in terms of buffs/nerfs affecting Rell directly

Buffed Matchups:
Akali is gaining 30 base health which won't really affect much besides her survivability

Nerfed Matchups:
Zac will be getting his HP regen nerfed which considering he heals a ton off his blobs is a very good thing

Rell is not the most dangerous champion in the game to play in the toplane, but she can easily be one of the most annoying and hard to fight champions in the right hands

You're taking on the role of the engage tank that can not only hard CC the enemy team for a good while, you also have one of the best engages in the game, and also help make tanks squishier by removing their resistances and even better, add them to your own to make you bulkier

Between her stronger than average trade potential once shes sitting on boots and a component, her impressive CC and hard engage potential, her tank power to withstand it all and the impact she can have on any team, Rell is definitely one of the most underrated champions you'll see and playing her top can make her shine much more than in the jungle or supporting an ADC

Trust me when I tell you that this is far from a troll choice. Rell may not be a traditional toplane champion, but she is easily one of the best tanks to play in the toplane for yourself and your team

Rell is meant to do a bit of everything here, so i'll break it down as best as I can here

As Rell, you can roam if you see an opening but I recommend that only once you hit Level 6 and your TP is up. Otherwise, here's what you should try to do during lane phase

• Hold Wave Close To Your Tower:
  This is a good strategy to make it slightly harder and riskier for enemies to get CS and attack you, especially if they thrive on being aggressive.
  Rell has really good CC, so if they decide to attack you under tower, you CC them to hell while tower kills them, or if they're trying to get CS/Trades, you can remount them under tower for a bit of easy poke
  Once you get at least the boots you need and the component item you plan on you can risk pushing in the wave toward the enemy and trade alot easier since it's harder to damage you, but that also does vary from champion to champion so make sure you know your own limits
  
• Assist your jungler for scuttle, void and grub secure if possible:
  I get that you might want to sit near the wave and soak in the exp and all, but it's favorable to your jungler to try and help secure the scuttle crab early especially because not only is there a chance for an early kill and/or to force an enemy spell out, but you also get on good terms early with your jungler meaning there's a higher gank chance, you're on friendly terms for objectives and you've helped secure a possible lead that they need to get in the game properly
  
• Short Trades:
  This ones obvious, yes, but not alot of people really respect Rells trade potential since they see her as a support meat stick. Especially with grasp and shield bash with your E your poke can hurt quite a bit in the lane phase.
  The best way to poke? If you took grasp, just get it charged, dismount engage to CC them, Auto for grasp/shield bash damage, Q then back up. You can E if you want to as well for the burst damage but it isn't always necessary
  Like I said before that once you get the proper component and boots you need, your trading potential can go a bit longer based off the matchup so it all varies on how you handle it

Mid & Late Game Objectives:
You're out of lane phase, you're roaming, you're just trying to help your team at this point get objectives and end the game.
Optimistcally, your tower is still standing and so is your enemy laners. How is that optimistic? Because by this time you've denied them as much platings as possible, denied a tower destruction and kept your laner from snowballing or being too far ahead

So what should you be doing here?

• Engage For Your Team:
  As I said, Rells engage is one of the best in the game for starting fights. If you know a team fight is about to break out, or you wanna peel for a teammate, you must engage first within reason.
  Your CC is invaluable and holding enemies still so long like that will definitely give your team an easier chance to get kills.
  Again, and I cannot stress this enough, KILLS AND CS DO NOT MATTER ON RELL AS MUCH AS OTHER LANERS.
  You don't need to give up kills or stop CSing entirely, in fact I encourage you to CS on downtime, but your overall bulk power in some 1v1s plus the amount of engaging you're doing [as long as it goes well] will keep you in the game and provide you with the gold you need for items
  
• Do NOT Splitpush. Assist with Objectives:
  Rell has little to no tower damage aggro even if she takes demolish and it's a waste of time for both you and your team to be going into a lane and trying to take down a tower.
  The main objective for you is to try to be at the objectives you can afford to be for the incoming fight and try to help take them as soon as possible.
  If you're not there your team may not have a frontline and that puts them all at risk of a 4v5 if you're not careful
  The only time you should ever be seen trying to solo take a tower is when it's your lanes tower and you can afford to damage it, or if you're trying to take down a low health tower nearby after a good team fight
  Once an objective is taken you can either walk with your team or TP to a tower if you notice a laner [usually it'll be yours] trying to sneak a tower for gold
  
• Defend your Teammates:
  You clearly have the CC, you have the power to save them, you just have to be cautious about it.
  A team fight is obviously gonna get hectic, but sometimes the aftermath may have a late arrival or the fights split apart.
  Don't bother chasing a kill if you're alone [unless they're a shutdown and you're 100% certain a quick ability or auto is going to kill them].
  You wanna rush over to your teammates and help with the aftermath so they don't die. If they're close to death and the enemy gets a shutdown, not only is that bad depending on the champ, but then your team may have to wait to get objectives done longer than what they did if you had just let a kill get away.

Do not forget, you are the teams tank.
While you might be the carry when it comes to engaging, you are not the powerhouse carry in terms of damage so don't always think you have to greed for kills.
You'll get your fill on assists and sometimes kills eventually but for now all that you need to worry about is making sure your team is protected and that the enemy is properly hard CCed for a great engage on your teams side

Let's go over Rells abilities, and teach you stuff you probably forgot or didn't even know about what Rell can do with these:

Passive: Break The Mold

Break The Mold is what helps Rell become a bit tankier. Her basic attacks and abilities reduce and steal targets Armor and MR up to 5 stacks for a total of 0.8%-2% based on level. During fights you're not only gaining resistances, you're taking them away from enemies too, making your team do more damage while also making it harder to damage you in the process

Q Ability: Shattering Strike

Shattering Strike is a pretty simple ability to think about: You thrust your lance forward and stun enemies for 0.75 seconds. What people forget about however is that it actually Shatters, not lowers, SHATTERS enemies shields. So lets say you're against a Mordekaiser. He's taking damage from you and your jungler in a gank, he uses W, so you use Q and instantly, his shield is gone and he can't heal. That leaves him to either flash, ult [if he hasn't] or die. Enemies [and sometimes me] forget that her Q shatters shields so enemy comps that rely on shields like Sion, Shen, Morgana, etc. are not gonna have a fun time

W Ability: Feromancy: Crash Down/Mount Up

Crash Down/Mount Up [Remount] is Rells main engage tool. It has two parts and 2 "forms"

Mounted: While you are mounted, your auto attacks are slower but your movement speed is faster. It's good for chasing to start an engage, activates your E passive, and lets you use Crash Down in your W

Crash Down: You become Dismounted, leap into the air, and after a short cast time, land and slide forward in an AOE knocking enemies up for 1 second and granting you a shield. This is Rells main tool of engage in every scenario as it helps get your CC setup for yourself or your team for a trade/engage, and can also use it with your ult for easier landing. Just remember: You're technically considered casting in this, so if you're hit with certain CC like knockup or stun, it will stop you mid-animation

Dismounted: While you are dismounted, you gain 12% bonus Armor/MR, 30% attack speed, a shield and 75 bonus attack range BUT have 10% reduced movement speed. In this form, you're obviously tankier and it's easier to auto minions if you decide you wanna try to CS a bit. You do gain a shield while dismounted, but only AFTER you use Crash Down. The shield does not decay either, so it will be there until it is drained from attacks or you remount

Mount Up: Rell becomes Mounted and gains 30% bonus movement speed that decays 2 seconds, and empowers her next basic attack to be basically instant, gain 100 bonus range. When colliding with an enemy, she flings them over herself and stuns for 1 second. This ability is not only good for single target chase CC, but also just overall making yourself a bodyblock wall for enemies trying to run away. You shouldn't be afraid to remount if you know you can catch the enemy. Also, Remounts toss counts as an auto attack, so it can proc Grasp and Heartsteel

E Ability: Full Tilt

Full Tilt passively gives Rell in Mounted form 5-50 bonus movement speed based on level, but is reduced by 50% while in combat. When Rell activates this, she powers herself and a nearby chosen teammate, gainging movement speed that ramps up over 2 seconds from 50% of initial value.
When within an empowered ally or enemy, the movement speed is increased. This is an insanely good chase or escape tool. Rells next Q or basic attack in the next 5 seconds also deals bonus magic damage based on the targets max health. Overall, this ability is decent for bonus poke and chase/disengage that can benefit a teammate greatly if used properly, and also makes your heartsteel/grasp proc stronger

R Ability/Ultimate: Magnet Storm

Magnet Storm is Rells ult that causes her to erupt in an AOE pulling enemies in range inward toward her, creating a gravity field that pulls enemies toward her, and deals magic damage every 0.25 seconds. This is not only one of her better abilities to create openings for your team to start fights, but also a good stalling tool for your team to rush over.
This ability can be paired with your W Crashdown. So the best way to use your ult is to use Crash Down then ult while mid-air. What happens is that you'll drag enemies in range toward where you're standing, then they will be knocked up almost instantly by your W making it near impossible to avoid.
This may sound hard to pull off, but really it's easy. If you're concerned you'll screw up, just go to the practice tool and use W then Ult, and you'll see it's not that hard

There are a few Rell combos that some people may not know about and some all of you know about. I'll try to explain the ones I've found, use and what scenarios they work best in

W Dismount+R CC Combo
Lets just get the obvious one out of the way: W Dismount into Ult is one of Rells most well known combos.
It's a great way to hard engage the enemy for your team, get your passive stacked up to gain/steal resistances, pull them in so they can't dodge your W and overall just a great way to keep them still while your team bashes them to death while they can't move [unless they're an ulted Olaf]

Q+Flash Combo
Not everyone knows you can wind up Rells Q and flash while it's charging up to thrust forward. It isn't the most practical of uses for it, but it can be done in two ways:
You can either use it to flash forward and Q them, stunning them in place for that split second for your team to get in or secure a very low health kill, or you can Q then flash backwards so that you can get a stun off while flashing away, or even better, if you predicted they'd flash after you, you can use that combo to flash backwards as they flash toward you, get a stun off and possibly escape

I will recommend the Q+Backward flash be practiced in the practice tool because it can be weird to get used to. At max auto range both mounted and dismounted, it's not possible to max flash distance away and land the Q unless they flash after you, so if you want that backwards combo to hit, you'll willingly have to avoid flashing max distance unless you're 100% certain they will flash after you instantly

W Remount+Flash Combo
This is definitely one of the better ways to secure a chase target so that they have to flash or die if you have a teammate helping you chase them down
The premise of this one is pretty easy to understand: W Remount, and as you're remounting flash on top of them so that your auto hits and you toss them behind you for your team

I will disclose that Remounting then flashing, or flashing then remounting can work, but Remounting then flashing is an easier way to secure a grab on them since you won't have to wait for your remount right when you get on top of them. That split second you're waiting for remount could easily determine if they get away or not.

Not to mention from my testing Flash into W Remount seems to be slightly delayed depending on if you hit the buttons fast enough so that's up to you how you do the combo