When I downloaded this mount it came with a new .u file called Rider.u
But even with it in the system, it seems that the client calls Strider when I click to mount the pet.
From what I understand the mount file is inside LineageMonster.u but I can't compile it because it always has different errors.
Well, I tested it now with this LineageWarrior.u file and it just gave the same error.
I wrote to you on Discord earlier, if you can help me it would be nice, it would help me a lot.
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It's better to create a new .u file, no need to recompile LineageMonster from scratch; that said your 'LineageWarrior.u' is missing a class called 'LineageRidePawn'.
add this file to your compiler's system and try again
also, here's a nice guide in case you haven't checked it out yet