Continuity Nod / Kung Fu Panda 2

• A major plot point revolves around Shen leading a massacre against the panda village in an attempt to prevent the Soothsayer's prophecy, and how his actions inadvertently caused a younger Po to end up in the Valley of Peace, eventually growing into the warrior destined to defeat Shen. This directly parallels the catalyst of the first film's events, when Shifu - by sending a messenger to ensure that Tai Lung wouldn't escape from prison - indirectly caused the latter's return to come to fruition, with the Soothsayer's narration even paraphrasing Oogway's warning.
  Oogway: One often meets his destiny on the road he takes to avoid it.
  Soothsayer: [Shen] set out to change his fate, but what he did next only sealed it.
• A kid playing with a Po figurine in the opening scenes says "Enough talk. Let's fight!", which is Po's first line in his fantasy of the first film.
• There's also several in the opening fight in with the wolves. Many shots and elements of the whole scene match up with the 2D opening dream sequence of the first movie, including Po's "Feet of Fury" technique.
• Despite the difference in art styles, Shen's wolves bear a strong resemblance to the wolves from Po's opening dream from the first film, potentially hinting that he always had some subconscious memories of when they attacked his birth family.
• The Soothsayer uses acupuncture needles to cure Po and mess with his facial expressions in the same way Mantis (unintentionally) does in the first film. It's the only way she can get him to take his medicine.
• Speaking of Oogway, all of Po's Character Development was about him finding inner peace, by accepting his past and not letting it decide who he is now. This was the lesson Oogway tried to teach Po in the first film so that Po would not try to flee his destiny as the Dragon Warrior.
• When meeting the Furious Five in the first film, Po commented that Mantis was about the same size as his action figure, unintentionally offending the latter. When pretending to surrender to Shen's wolves in this film, Po uses his Mantis figure as a decoy and places it inside the cage, allowing the real Mantis to hide undetected and sabotage Shen's cannon.
• Oogway's wooden staff, broken by Tai Lung in the first film, has now been repaired and is used by Master Shifu in this film.
• The archway above Mr. Ping's noodle shop has visible cracks and fillings, having been repaired after Po threw Tai Lung through it during their battle in the first film. The shop itself has also been renamed "Dragon Warrior Noodles and Tofu", implying that Po's success also encouraged Mr. Ping's dream of making tofu.
• Po slugs Monkey, then apologizes, when the latter unexpectedly appears inside the dragon costume. In the first movie Monkey automatically slugged Po then apologized after Master Shifu freed him from the nerve-strike paralysis.
• A subtle one: Oogway, in the first movie, notes how Po eats when he's sad. Here we found out that he was hidden in a crate of radishes as a cub, right before his mother was supposedly killed. By the time the crate got to Mr. Ping, Po had eaten the entire contents of the crate. Which also explains why Po is slightly thinner and less hungry than before. Ping even worries that he's lost weight.
• Master Flying Rhino is mentioned, for donating his armor to the Jade Palace in the first movie, and as the father of Thundering Rhino here.
• Oogway once said "Yesterday is history, tomorrow is a mystery, but today is a gift. That is why it is called the Present." That's the theme of this movie. Po let go of his parents' and species' massacre when the Soothsayer told him that fate balanced the scales and eventually gave him a happy life with Mr. Ping, who cares for him and loves him as if he was his own blood himself, and his friends, who helped him achieved his most cherished dreams, especially Shifu, who has all but become a second father, and Tigress, who may be falling in love with him. What happened in the past is history and he might not know what will happen in the future, but his life in the Valley of Peace is a literal Present.

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