I have seen some people post about having trouble in this part of the game (especially the Swalot) that I myself have experienced and have brought it upon myself to make a topic on some helpful tips on getting past this area. All I have to say as an example to say this off is one move.
Perish Song
In my first playthrough, (I have played through this masterpiece twice, once in episode 15 and again in episode 16) this was the answer to all of my problems and Absol was the harbinger of that answer. Make sure to have an ill-fated doll on you when you enter into Agate City for the first time. For as "ill-fated" as the doll is it will bring you good luck later in the game as a key item for getting Absol (as well as poke balls for those who aren't the sharpest tools in the shed). Having the Absol boi along with him learning Perish Song (which he should learn by either getting him to level 65 or via move relearner (there's one in the circus and yes requires a heart scale)) and some cotton candies. Taking down PULSE Avalugg, Pulse Swalot and even MEWTWO (yup you are gonna come across that guy). If you have trouble with anything else at that point of the game or need to find some other way of beating those Pokemon because you either forgot the doll or didn't catch the Absol (you monster), ask, that's what this forum is about and either I or some other good samaritan will be there to answer the question for you.
Now out of all of this, I have a question to ask: HOW DO YOU SHOW OFF YOUR POKEMON TEAM!?!