Judging of how big the basket full of fish for Toothless' is and how big the fish are, there is no way 100 fish can fit in there as Hiccup mentions.
In the opening theme after Toothless does the sonic boom the other riders exclaim in amazement but in The Terrible Twos no audio is heard from them after Toothless' sonic boom.
When Toothless begins to fire a blast in the fire pit in Hiccup's house the steam inside his mouth is yellow, the steam inside Toothless' mouth is supposed to be blueish purple before he fires a blast.
Hiccup didn't even blow out the candle by his bed he just inflated his cheeks, also there is no way he could have blown at the candle from the distance between his bed and the candle.