is the ending 'u' thing actually a myth??

hi guys! so i heard this thing online that if you pronounce the 'u' sound at the end of words you sound like an anime villain?? is that true?? i'm so lost lol. also maybe this is dumb but do i need to roll my r's? i think someone said japanese r is actually a d sound but then my friend said it's an l. i'm so stressed about pronunciation now haha