The Turtles' Origin is Told

Donatello's Role
Overall Involvement - Major

The turtles face against a street gang called the Purple Dragons in an alley. As Leonardo puts it, "To my left, Donatello and Michelangelo follow suit with bo staff and nunchakus." Joining his brothers in battle, Donatello takes out one thug with his staff and another later, bludgeoning them in the head while mid air and kicking another in the chest. Once the gang is defeated, they are forced to flee when the police arrive.

Donatello helps Leonardo move the manhole cover and they return to the sewers. He and his brothers then listen to Master Splinter, who tells them of his origins and theirs. They proceed to act out their purpose, of avenging Splinter's Master Yoshi by killing the Shredder. Donatello follows his brothers to a rooftop where the turtles announce themselves.

The Shredder calls on the Foot Clan to fight them, at which Donatello attacks with his staff and says "These guys are good!". Bashing a Foot soldier in the face, he gives Leonardo a boost, who then takes out the last of Shredder's goons. When the turtles take their shot at the Shredder himself, attacking one by one, Donatello goes second. He is arguably taken out the fastest, while also receiving the most grievous wounds in being sliced by Shredder's bladed gauntlet before he is kicked away. Shredder comments on that Donatello left himself "wide open" and that he was "much too slow".

Once they start fighting together, Donatello knocks off the Shredder's mask and hits him in the back. However Don is soon caught off guard and kicked away again while saying "This is the end for you, Shred--". The Shredder makes a comment on Donatello being "overly confident", and even Leonardo says that perhaps he is, but perhaps not, once Leonardo runs his sword through the Shredder's chest.

The turtles offer Shredder a chance to redeem himself by allowing him to end his own life, however he threatens to take the brothers down with him. Revealing a thermite grenade, Donatello quickly throws his staff and knocks it out of his hand. Saving the four of them, while also inadvertently killing the Shredder as he falls from the roof top. In the aftermath, the turtles express their exhaustion, and Donatello mentions that he'd like some tea.

Quotes

 * "These guys are good!"
 * (But we) "...Are ..." (better!)
 * "This is the end for you, Shred--"
 * "No!"
 * (A hot bath would be nice ...) "...And some tea ..."