At the end of that OVA, Terry goes up against Mars and starts to seem to combine his techniques. For example, he uses the Sempu-Ken (that tornado punch) with a pair of Burn Knuckles simultaneously, and ends up getting even more out of it. Plus, his 'regular' techniques have a lot more oomph to them. He uses another Burn Knuckle that shrouds his entire body with blue fire, not just his fist, and ends up resembling his Power Dunk move from later KoF games.

The final attack that takes out Mars, to hint, looked like he should have said 'Are you okay?' at the beginning of it. Basically, Mars goes to hit him, and Terry punches straight into Mars' attack, causing an immense explosion of energy that overpowers and obliterates Mars. It resembles his in-game ultimate move, the Buster Wolf.

So in comparison to his moves/power levels previous to this fight, he certainly was operating at a higher level of power as well as chaining moves together in a way he hadn't before to produce greater effects. And pulled out what was effectively his Buster Wolf at the end, basically creating that technique on the spot.