my 2 cents...
On June the 17, 1462, 60.000 ottoman regulars and 20.000 irregulars were about to attack Vlad's capital. That night, he led his 30.000 strong army into a surprise attack, aimed at killing Mehmed II. OTL, this failed, although they killed 15.000 Turks for 5000 of their own, but suppose everything goes according to plan.
Confusion is greater with the Turks even fighting among themselves in the chaos, the other half of Vlad's army that was supposed to attack does so at the best moment, the sultan is killed and the Turkish army routed and then consistently attacked as they try to retreat across the Danube.
Events play out in such a manner that a civil war breaks out in the ottoman empire.
Vlad however loses his throne shortly after to a boyar coup and flees into Moldova to his cousin Stephen III (OTL called the great). Together, they march into Wallachia where they achieve victory, but both Stephen and his son are killed. On his deathbed, Stephen appoint Vlad as his successor.
Vlad goes about killing whatever boyars oppose him in both Wallachia and Moldova and promotes lesser one into positions of power.
Then suppose the crusade that had been planned is finally launched, with the pope and the king of hungary hoping to take advantage of the temporary ottoman weakness. With a huge amount of luck, the campaign is successful, with several territories south of the Danube going to Wallachia and the Ottomans split up into various states and forced to pay tribute.
So, does this qualify as meeting the challenge ?