Also, there needs to be a better way of gaining legendary and epic shards than to buy them. Does the developers even read these comments?

1) levels are the same. could be anything from different masteries, to changing gear, to faction guardians changing speeds/stats etc. that is to say, it's 100% on your end

2) getting to NM/UNM clan boss and farming top chest everyday gets you a good supply of ancient/void/sacreds, then there's farming normal/hard Doom Tower as well as fairly consistent free login legendaries (on top of the 270 days where you get several legendaries, epics, etc.)

Chances are you removed a piece of gear or changed something on one of your champions without realizing it. If you post a screenshot of your roster we can help you build a team to easily clear those levels. 

Thank you guys so much! I appreciate the help. Currently, I can't screenshot on my laptop cause the images just don't load. ): The Dragon's Lair stage 13 is what I need to pass more than the Sand Devil stage 1. I have a pretty decent amount of champions. I mostly use Elhain, Deliana, Foli, Ultimate Deathknight, and Sun Wukong. 

How do you have WuKong built? WuKong and UDK alone could probably take down Dragon 13. 

I always forget what a pain it is at the start to upgrade everyone's masteries. Do you have the masteries done for UDK and WuKong?

that's funny. I get top chest in UNM, NM, and brutal daily and in the past 2 weeks have only gotten 1 sacred shard, 0 lego books. The drops from Clan Boss have drastically dropped in the past 2 months, and not just the sacred shards i'm talking good drops in general. 

RNG, sample size, probabilities, etc.

The masteries was for sure an issue, I completely forgot about that. But also the champions chosen. I feel like I couldn't pass before cause I didn't have any champions that helped with support and defense enough, I was only caring about how many hits to make. As for WuKong, he is at lvl. 50 with masteries mostly in offense and with righteous and cruel artifacts at lvl. 12. 

BUT I finally passed level 13 in the Dragon's Lair using Elhain (lvl. 60), Ultimate Death Knight (lvl. 60), Scyl (lvl. 50), Adelyn (lvl. 50), and Kael (lvl. 50). 

Thanks for the help! 

Now the only thing is to try and get skill books... :(

Your bigger problem is that you are using level 50 champs. Which is almost certainly a sign that you are doing many other things incorrectly, such as wasting resources leveling/ascending random rares and epics that aren't useful, or trying to do content with champs that don't have masteries, or using the wrong kind of gear, etc...

If you want better advice, you'll need to post pictures of your champs and the gear they are using, or, if not, verbally describe the items - especially the bottom-row ones (gloves, chest, boots).

I beat the stage with them. And I fixed the mastery issues if you seen. And I've been getting rid of champions that are not useful. So, no I'm not doing things incorrectly.  

There are plenty of lvl 50 champions that can solo levels or a team. 

Also, it's hard to level up champs that are level 50 when you need to use the legendary shards, that barely drops unless you buy it out of of pocket, to get other lvl 50 champs and then on top of that you need to use coins for them to level up or level up other chapions to 50 but again you need use a lot of resources. Gears aren't the only thing to question. Like I said, we need skill books to progress our champions as well. 

I'll be sure to post pics when my laptop isn't acting up.

You are doing things incorrectly, not to be rude.

You should have a dedicated campaign farmer that can do 12-3 brutal in under 10 seconds. This is where you will spend a lot of time early game preparing food to rank up champions worthy of ranking up. You should only be investing in champions that will be of significant use early on to get you into farming level 20 dungeons and more importantly clan boss.

You mention skill books and shards being hard to get. It will take time but once you are getting top chests from unm, nm, and brutal cb daily you will get plenty to really power up your account.

I would suggest posting screenshots of your champion roster as well as a couple screen shots of the gearing on your level 60s.

You are going to hear things you dont want to hear...ie probably wasting resources on garbage champions as well as gearing champions poorly. If you want to progress the account harsh criticisms will get you there and there are some very knowledgeable and helpful people on these forums thst will give it to you.

Just one other thing to add ontop of what zed said - why would you need legendary shards to upgrade level 50 champs? I very much hope you aren't thinking that you need to use champs of the same rarity in order to upgrade their rank. You can, and should, ONLY be using 1* and 2* champs to rank up everything.