The final scene of Episode 18 was used in this episode.
The Trix weren't expelled since the events of episode 16 never happened in the last episode.
During the moments before the final battle, the sky was clear as opposed to it being cloudy in the original.
In the original, the Right Tower of Alfea was destroyed by a monster, but, in the special, since the final battle didn't happen until the episode 26 segment, the tower was left intact until Stormy destroyed it while trying to break the barrier.