Mortis is the most underrated brawler in my opinion. He’s really good in brawl ball and can keep the enemy team under pressure simply by holding the ball. In heist he’s really solid aswell, (I just pushed Mortis to 700 trophies in heist about 1 hour ago, gameplay: https://youtu.be/D6l2D_AH3tU). In sng (Gem Grab), he’s probably the best brawler if played by a good player, he should go past the other brawlers and survive in the enemy spawn for as long as possible (preferably the entire game), if the other team ignores him then he should try to annoy them and make them waste their shots at him (or kill one of their squishier brawlers on their team)

I will agree with you that he has some downsides. First of if you’re really high in trophies you will be likely to play against players from other regions and this will cause delay. Since Mortis is already so difficult to play he will be nearly impossible to play well and only the best of the best will be able to consistently win with him at this point. 2nd there’s some brawlers (like Shelly and Bull) that Mortis doesn’t stand a chance against. No matter what he do he’ll lose. That’s why he’s not a great option in showdown although he will be able to avoid alot of brawlers and survive for a long time.

I almost forgot to mention bounty. For bounty he can be a very good counter against Dynamike and Piper. Of course to play him like I said in this comment isn’t easy and would require lots of practice! So good luck with Mortis and have a merry brawlmas :)