Which Scott Adkins character would come out on top in a fight — Undisputed's Yuri Boyka or Casey Bowman from Ninja? By far the two most iconic characters that Adkins has portrayed in his career, each one brings his own set of strengths to a head-to-head match, with Boyka being a force of nature in the MMA world and Casey being a genuine Ninjutsu master. Comparing each martial artist side-to-side, a face-off between Boyka and Casey would likely see the winner just barely emerge victorious — and it would be one hell of a fight.
Obviously, Casey being a ninja would mean that a real fight between them would need to be on a level playing field, with Casey's skills in Ninjutsu weaponry and stealth tactics greatly tilting the odds in his direction if he could simply launch an unexpected attack in a dark alley or a forest. Even accounting for this, a Boyka versus Casey showdown is a tough one to call. Both bring their own respective strengths, and despite boasting the title of The Most Complete Fighter in the World, Boyka actually has a significant weakness.
Between the two of them, Boyka is more vulnerable to letting his pride get the better of him, as seen in Undisputed 2: Last Man Standing when he went up against Michael Jai White's George "Iceman" Chambers. Despite being far less versed in the techniques of MMA, Chambers was able to defeat Boyka, leaving him with a bad knee to overcome in Undisputed 3: Redemption. By the same token, that film and Boyka: Undisputed also showed that he was capable of learning from his shortcomings, and while Boyka has faced numerous opponents who gave him very difficult fights, Chambers remains the only one to outright beat him, and Boyka would very likely win if they were to fight once more.
When it comes to Casey, he was shown as a formidable but much less ruthless fighter than Boyka in the first Ninja. However, after the loss of his pregnant wife Namiko in Ninja II: Shadow of a Tear, Casey transformed into a beast let off the leash. Of course, blind rage can also be a hindrance in a fight, and perhaps because of his loss in Undisputed 2, Boyka showed a greater capacity to channel it to his advantage. This means that Boyka's pride and Casey's anger gives either of them something to exploit in the other.
At the same time, both men have shown an ability to take great punishment and keep going, with Casey being stabbed through the arm in Ninja and still managing to defeat Masazuka in the end, and Boyka getting past his bad knee in Undisputed 3, and even surviving several bullets to the torso in Boyka: Undisputed. When looking at the two in terms of sheer fighting skill, it's frankly a wash between two exceptionally skilled martial artists. In all, a fight between Boyka and Casey is a very hard one to predict.
In the end, though both have their share of vulnerabilities for the other take advantage of, Boyka would probably be the winner in a fight between the two. Boyka has demonstrated remarkable endurance in his past matches, and his aggressive, vicious, martial arts fighting style would give him an edge. Nevertheless, it would be a very, very slim victory, with the two leaving each other barely able to stand by the end. In a face-off between Yuri Boyka and Casey Bowman, The Most Complete Fighter in the World would be the most likely to emerge the winner, but it would be easily his toughest fight and most narrowly earned win.