Some TMNT stuff really isn't for little kids.
A version of Donatello from a possible future in which Shredder and Krang had conquered most of the world. The Turtles encountered him in the IDW continuity miniseries Turtles in Time, when their fourth sojourn through history took them to a futuristic Manhattan that was ruled by Shredder.
The Turtles were forced to flee into the sewer, where they found an aged Donatello, who hadn't left the lair in years. He revealed that his brothers were all dead, having continued the fight against their enemies. He himself had only survived this long because he had given up against the impossible odds. This horrified and disgusted the younger version of Donatello.
He reluctantly agreed to take them to the place where the leadership of the Resistance was about to be executed. When a person in the crowd struck him in the fight, he began fighting with his bo for the first time in many years. Before leading the Resistance to his lair, the old Donatello told his younger self that this was only one future, and that he "maybe" could find a way to fix it in the past.
Back in his lair, the elderly Turtle was told by a war-hardened Woody Dirkins that the Resistance needed fighters and leaders. He pulled his old purple mask loose, and seemed to be considering it.