This is a very bad way to end the original Thomas & Friends franchise, and here's why.
To get the elephant out of the room, it's an extremely disappointing series finale of an iconic show that ran for over 30 years. To make matters worse, there is NO chance of the original show ever returning since Mattel has screwed every fan over since the announcement of Thomas & Friends: All Engines Go because they wanted to pander to little kids and cannot accept that older people enjoyed the show as well as children do. Ultimately, this means that the Thomas franchise as people know is dead and gone forever.
Although Thomas is not really unlikable in this episode, the character choice to have him be the main role of the episode isn't 100% necessary here because Nia was already given the job to help out for the animal park in the episode, "Nia and the Unfriendly Elephant". Nia would have been the right role since she did manage to help out a stubborn elephant that wouldn't go onto her flatbed.
The concept of the engines dressing up as animals is very stupid on practice and is another example of bad writing from this era. By now, who even cares about concepts that are only existent for actual merchandise and not actual episodes?
The plot is rather weak, uninteresting and very boring. Similar to other episodes of BWBA, it stands out for all the wrong reasons.
Speaking of the plot being uninteresting and boring, the pacing is boring because of how sluggish it is. Of course, there are slow paced episodes in the series, and they do a good job with the slow pacing in some episodes. But here it feels just as sluggish and bland as "The Other Side of The Mountain".
Despite appearing for a couple seconds each, Percy, James, Diesel, and Gordon are all unlikable in this episode, as they make fun of Thomas for his monkey costume he has to wear. Percy is also very out-of-character here, as he laughs along with the other engines about Thomas' monkey costume, when he is supposed to be Thomas' best friend.
Just like "The Magic Lamp", the episode's existence is kind of pointless because Mattel already released toy packs made for the Motorized merchandise range relating to the engines being dressed as animals with rolling stock included. Let alone make the episode just a 7 minute long run advertisement than just an episode.
Because of the statements made, "Thomas' Animal Friends" feels very rushed and is overall a very poor way to end the original series.
At least Thomas is still a likeable character.
This is a very bad Thomas & Friends finale episode. Please do not watch.