Shantanu and Devavrat
The following variation is according to MBH Serial. These incidents are not mentioned in MBH.

Shaantanu came back happily to his chariot. When Saarathee saw the prince coming, he hailed the prince. The prince said - "If you want to hail, then hail to Hastinaapur, because the kingdom is always higher than king and prince." When they came to palace, people welcomed the prince very enthusiastically. 

Shaantanu said to Devavrat - "Putra, Share your knowledge with me." Devavrat said - "Father, Knowledge brings humility, humility brings ability, ability helps in getting wealth, wealth helps to fulfill Dharm activities, and Dharm activities give pleasure and comfort and happiness."

Shantanu asked - "What Vashishth Jee taught you?" Devavrat said - "I learned from him that as a bird can fly only with two wings, in the same way a human being can also fly with two wings: his one wing is Karm (actions) and the other wing is Gyaan (knowledge). If any one wing is not there, he cannot fly. It means he can not get Mukti by one wing only."

Devavrat further said - "If you start any project, then take rest after finishing it only, otherwise the project will finish you." Shantanu asked - "And what Shukra ethics says about this?" Devavrat said - "Only the result of the project can tell you that the beginning of the project was auspicious or inauspicious?"

Shantanu asked - "And what Parasahuraam Jee taught you?" Devavrat said - "He said that to obey father's orders is the highest Dharm."

Shaantanu asked Devavrat - "Putra, Devtaa must also entertain themselves. What are the means of entertainment in Dev Lok?" Devavrat said - "They also play Chausar (dice game), but they have a different kind of Gotee. Their Gotee are human beings, and they ask Kaal (time) to throw dice, then play Gotee and beat Gotee."

Once a trader came with a horse and claimed him the finest, Raajaa said that if they could find any other horse even equal to him, then he will get death sentence. Nobody could ride on that horse Then Devavrat asked the permission from Shantanu to handle him, which he readily gave, so Devavrat took him, put the saddle on him and asked the permission to ride on him for some distance. Raajaa got very happy to see this, and gave him permission. 

Devavrat went a little far that he saw a king coming to his side with his army. He was Shaalv Kumaar. He challenged Devavrat. Devavrat fought with him and defeated him in a few minutes. He brought him with him to Hastinaapur and handed over him to his father. His father wanted to give him death sentence but Devavrat said - "Pitaa Jee, Enmity doesn't end with death. He should be pardoned and freed. Then he will be our friend." Shaantanu got very happy with his judgment and did as he said.

After this event Shaantanu declared him the Crown Prince and completed the formalities related to it. The time passed and Devavrat grew in a fine young man.