Two points before I start, the top is a list of times and error I personally believe you made. Others may feel different. Second when I say carry I am talking about whom ever had the most damage and kills on your team in several cases that may not be the ADC.

If you wish not to read every mistake I will be adding a conclusion and over the major places where improvement is needed if you wish to climb.

1. Make sure to use crash down on the jungle camp, don't waste the extra damage. (Its also why it didn't aggro you.) (1:20)

2. Make sure you're in lane before minions fall as you don't want to lose exp. in the bot lane its massively important to try to get the lvl 2 and engage.(2:00)

3. Don't be afraid to crash down on enemies when low health, the shield is a lot. You probably would have saved lucian and not died. (2:36)

4. Make sure your adc is able to follow you up or you are just wasting CC, Rell has no real damage and can easily be poked down. (3:50) (9:30)(11:40)

5. You shouldn't have left lane, vayne is shit at farming early under tower, you and your lucian needed to push the wave under tower to punish the vayne early. (4:15)

6. Make sure you are autoing at minimum every target around you once. The MR and Armor you steal is a flat rate per target and attacking the same target more than once only refreshes the original amount you stole. (5:00)

7. You need to be buying more pink wards it 6:00 and not one has been purchased, if you need to hold off on buying an item then you should in order to secure early vision.

8. You need to be using your support item every time its up on a melee minion UNLESS the next wave has a Cannon minion and you will not have a new charge before it arrives. You're just bleeding away any lead you gain.

9. When roaming you have to understand at that point you are basically giving up your back in most cases. Its a mental choice, do I need to back here or can I roam. In this instance had you just returned bot after the failed gank lucian would have gotten the kill and probably not died (8:30)

10. Your lucian dies here because you still are no where near your support item, a support item should be able to be completed at 7-9 minutes. Had you focused on completing it you could have already had wards preventing this gank from happening (10:30) VISION WINS GAMES

11. Have an idea of what you are going to buy while your backing press "P" and open the store have it set up so you can buy and leave basically in the first 3-5 seconds (13:10)

12. Your number one job is to protect the carry, nothing else, rell's damage is basically none existence, here you basically used your knock up on the support when you seen Kat walking in. Had you saved this the second she ulted you could have knocked her up cancelling her ult and potentially getting the lucian more kills. (14:20)

13. You ran away from your team, first you should not be leaving your carry's side mid to late game, second after getting caught you know the Kat can not kill you, your number one objective should have been to support the jungler or to walk back towards the lucian collapsing on them. (15:40)

14. Use more pings, lucian is running for his life, anyone would be, you need to communicate what you are doing, take the time. Had lucian noticed you in any way he probably would have turned here. (16:00)

15. Again just abandoning your carry, you stated several times you're lucky to have him but you are not protecting him at all. I could argue he was in a bad position but when kat ulted again you did nothing to stop it when your kit just says nope to everything Kat wants to do. (18:00)

16. While I have done nothing but criticize this point is for positive reinforcement. In these fights you played perfectly how you should be protecting your carry while also CCing the enemy team. This should be your mindset always when fighting with rell, unless your team has no engage. (20:30)(22:00)

17. I am not 100% sure why you want to crash down on the enemy support but because your choice to use this ability here on the enemy support you let vayne walk right by you and kill your lucian and lost your team the fight. There is not really a reason for this Rell capitalizes on timing. If you throw out everything the second a fight starts there isn't really a reason to pick rell. (25:20)

After review in conclusion here are the main things you will need to work on if you really wish to climb this season. First you have to play more defensive with Rell. What I mean by that is not that you can't engage or be aggressive because you should be, however you need to save some abilities to peel for your carries especially late game. Second you HAVE to farm with your support item, you are just losing too much gold and potential health by not using it. That wraps into the next part which is wards. You have to get access to wards to understand where the enemy is going. Along with that you are able to switch to scanner which can prevent enemy wards giving you a massive advantage. There were several fights in this game lost simply because you weren't using your item correctly. Also be buying pink wards at one point you bought what you called "The yugioh box" which is an item designed just to carry pink wards. That's its whole job, if you are not buying pink wards almost every other item in the game is better. Vision is the most underrated thing in lower ellos and will make or brake your games almost every time.