There's a pretty firmly-established rule in movie sequels that you have to escalate things to improve the entertainment factor. Sometimes this leads to over-reaching, shark-jumping changes that ruin everything, but the best sequels manage to balance escalated stakes with character development where there's less need for exposition.
And within that successful trend, there's a specific type of movie sequel that dials up how badass certain characters are for maximum impact, whether by increasing their cool factor or their power levels.
Sometimes characters disappear after their first outing and end up with a huge injection of badassery (that occasionally comes absolutely out of nowhere as an added bonus). And in most cases, that improves them as characters significantly...
10. Luke Skywalker - Star Wars
Star Wars has a couple of surprise badass turns throughout its history - partly because of George Lucas' fondness for underdogs discovering they're the Chosen One or the Galaxy's Last Hope and stepping into those daunting boots. We've seen Han Solo go from cool anti-hero to bona-fide Best Guy In The Universe, ewoks show surprising steel and Anakin Skywalker goes from grumpy emo to the fiercest foe the Resistance has ever seen.
But no character arc fits the Suddenly Badass trope quite like Luke Skywalker's.
He starts out as a milk-drinking, scrap-salvaging farm boy who overcomes the odds to destroy a Death Star (despite CLEARLY still being very green at the end of the first movie) to being a straight princess-rescuing badass ace pilot whose exploits are as stunning as his ability to shake off all doubts levelled at him. Obviously, his trajectory was always going to go that way, but it's still quite startling how quickly he shrugs off the underdog status that defined him in the first movie.