As much as I like to say I enjoyed it, I can't. The previous eight episodes have all been good to amazing, but this one is the first (and hopefully only) clunker of season 3.

First, some things I do like:

1. Rainbow Dash's character. Dash has shown a bit more of her sympathetic side lately, but here is where we saw her cockiness, eagerness, and going in way over her head. Her blurting out her own novel idea as well as Applejack's was hilarious and gave me the most laughs throughout the episode. From the way she's behaving, she's grown into liking action novels more and more. (Bronies, she gave you her idea. Write it!) But I also laughed hard at the fact that Rainbow Dash had to keep her promise and demolish the tower. Mission failed! >)
   
2. Twilight's concentration. Over the past several years (in the canon), she's shown a huge desire to learn, grow, and be invested in doing her very best in her assignments. If there's one thing she can get into, it's get into a zone of deep concentration. It fits extremely well into her character, and I can really relate to her in this scenario.
   
3. Rarity's compassion for Spike. She knows Spike's mud pie is absolutely disgusting, but she is good friends with him, and their friendship has grown considerably since the series premiere (especially Secret of My Excess, my second-most favorite Spike-centered episode behind Dragon Quest). She spat it out, but only when Spike turned away; she doesn't want to hurt his feelings, and he can get pretty reactive. It's obvious she cares for him as a very dear friend.
   
4. The Mane 6's "Master Plan" to break Spike's "code" failing miserably. They were desperate to break Spike's code and decided to have Applejack get attacked by a timberwolf puppet. But they forgot big time about Spike's advanced intelligence; he's naïve, but he's not someone who gets easily fooled, and that trick almost bit them each on the flank. And it nearly bit them back harder when he rejected the timberwolf breath late in the episode. Sometimes, it's better not to cry, "Wolf!"
   
5. The timberwolves. They're extremely detailed, but very well-done. Given the nature of the Everfree forest, there are many scary, dangerous creatures to watch out. The timberwolves looked scary, dangerous, and powerful. And I'm not sure if Spike's flame wouldn't have worked, given the spell-casting substances the wolves had.
   

Now the two things I didn't like, starting with the smallest:

1. 
   
2. Pinkie Pie's erratic character before the last commercial. She's bubbly, excited, happy, slapsticky, and random. But given the nature of the scenario before the commercial, it didn't fit her one bit.
    
   Her antics prior to it fit her really well. Too Many Pinkie Pies explored her sensitivity, care for her friends, and commitment. Wonderbolts Academy had her behave obsessively, but Pinkie Pie and Rainbow Dash have shown throughout the series that they have an extremely close relationship. Each of the Mane Six are very great friends, but some are closer than others. Pinkie Pie is extremely close with Rainbow Dash, and as Wonderbolts Academy is tiring and strenuous, she doesn't want that bond to separate.
    
   But in here, it didn't fit. She would've taken the whole scenario a bit more seriously; if it were slapsticky, it would've been more toned down, as she's a character with tremendous depth and understanding of serious circumstances. She was too hyperactive and happy in this case.
   
3. Spike himself. He has been in the spotlight so much more this season, and he's had several small but very important roles: getting the Crystal Heart back to its rightful spot (only to be rescued by Cadance), finding the book about the Mirror Pond, and keeping the team composed in Magic Duel. Prior to season three, for the little spotlight he's had, he's had great character development, particularly in three season two episodes: Lesson Zero, Secret of My Excess, and Dragon Quest. Season two was, honestly, the best season he's had, and season three continued to develop him even more. It wasn't the Mane Six (with Spike bouncing behind them). It was the Mane Six (with Spike crouching in front and getting a nice little hug from his friends).
    
   He didn't feel right at all in this episode. His eagerness wasn't the problem at all. He's a kid dragon, and kids tend to be extremely eager; boredom sucks. But it resulted in him being not only being continually clumsy, but also CARELESS. Spike is many things, but carelessness and continual clumsiness aren't either. Spike can be bored, eager, or excited however he wants, but he has known Twilight and the others for quite some time already. He's shown to have a somewhat advanced intelligence due to his talking, cunning, and line of thinking. Seeing him become so destructive (and not even be aware of how bad his clumsiness was at times) doesn't fit him at all. He has known the characters long enough to understand how things work for them, and he's able to understand each of their expectations, mannerisms, and personalities. Spike himself is also a very good cook, and I'm sure he'd know how to handle an oven as well as preparing fine ingredients for an apple pie.
    
   I think it would be much better if some things would've changed, Spike's carelessness especially. It would be having Spike be clumsy with the balloon, apples, and then the pig (with him actually being aware of it), but then AJ and Spike would have a chat telling him that he can help, but slow down and take it easy. Afterwards, Spike would help with the chores and perform well at them. If Spike were to ask for help, AJ would, and the two would make a fine team. Then maybe they can visit Rarity, and maybe he could help her out a bit, too, using AJ's advice and Spike's knowledge on his surroundings and expectations of how Rarity works around the Carousel Boutique. You can write the rest.
   

I was extremely eager seeing Spike get a much bigger role, as he and Rainbow Dash have been the two breakout characters this season (minus Scootaloo). Despite several great small things, the main plotline in Spike at Your Service just fell completely flat. Overall, this was a big disappointment. Worst episode of season three so far.

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Source: S03:E09 - Spike at your Service