Anyone have any tips on the GL mu? Or just in general? Really struggling against him
You can zone lantern out with air lasers and regular lasers. Be careful with his lantern, the trade favors GL, but you can easily avoid it by walking back and punish with regular laser, or you can go for a teleport if you make a read. Try not to summon trait in neutral bc he can react and use his ex lantern to blow you up, but if you get a knockdown go for it. Green lantern has to play a very reactive game to avoid being zoned out in this matchup, so i find that whiffing pokes is a very good bait against him, it can makes him mistime his roll or his projectiles, leaving him open for huge punishes. Trait helps a lot in the projectile battle, but don't get too comfortable throwing back to back beams when you have a parademon out since his ex lantern travels pretty fast and can hit you before the beam hits him causing you to loose your minion. You can condition him stay still and go for a mix when you have parademon out, but be extra careful with air teleports since GL has great anti airs and whiff punishers.
When he gets to mid range it gets a little more complicated, he can punish whiffed omega beams and blockd low lasers very easily, so be very careful using these tools. His normals are very good, but don't let him abuse his staggers on you, keep him in check with d1s, backdash or and mbb3. Also you can throw preemptive d1s whenever you think he's gonna dash/roll in and buffer darkseid's mb knee, it is safe and knocks them fullscreen away from you on hit. If you get hit and put in his oki mix delayed wakeup is your best friend, it can really disrupt the timing for his setups, making them easier to see. And if you don't have meter don't try to anti air him with d2, his jump ins are gonna beat it 95% of the time.
Green lantern loses the zoning battle and has to come in, he is not very good at chasing people down so you can exploit his weaknesses and mistakes while building meter to put him back in the same situation again. Plus darkseid still has access to his top tier mixup potential, and there's nothing GL can do about that other than guessing correctly. Darkseid also outdamages green lantern.