Disclaimer - first post but lurker for about a year, I’ve used this site and all of your inputs genuinely since I first came across this wonderful source of information and (typically) civil and knowledgeable discussions. I also don’t know if this has been covered in this light, I know many people have tried to help/teach others about how to make Rocket Battles easier, but hopefully my insight helps. That being said, I’ve noticed many people having trouble with the Team Rocket Leaders (most notably Sierra w/ double Lapras & Giovanni’s infamous Persian w/ bite)…
This is not a ‘ha ha I can do this in my sleep’ bit, however, I woke up this morning to the typical looming rocket loons (which, yes, I wake up a little early just to take care of the first round before work) and without thinking I jumped into battle with my & my gf’s phone while still in bed. I get the typical “prepared to be shocked” on my phone in which I prepare a pretty well powered-up Groudon and win pretty easily (used 1 shield on first mon, didn’t use charge until 2nd and didn’t charge it up, blasted final mon). My gf however was unfortunately met by Cliff, and she was still quite asleep.
I hand’t handled many of the Leaders for her yet, just kinda set her up with some good-typed mons with spam-able charge moves and let 'er rip on her own. I decided to lead with her shiny 1/12/8 2335 CP lvl ~30 Swampert rocking MS & HC since I could eat thru his Grimer slinging that mud, it allowed me to put huge shield pressure on him, and Hydro Cannon is just busted (I mean, have you ever watched it in PvE? The damage gets applied before the animation can even begin. Brilliant.).
Not gonna lie, I don’t even remember what else I decided to back Swampy up with, because I never got to that point. I beat Cliff with a sliver of health left, no shields, first mon. Now I know there’s a variety that all 3 Leaders and Giovanni can use, and I definitely lucked out on his choice of mons for our battle, but if you focus on just a few key exploits of the NPC PvP (Rocket Battle) mechanics you can even start with an Omastar w/ MS & RS to help you rock Sierra’s world (get it, cause, Rock Slide? Oh, forget it…).
It’s been explained numerous times by several sites (this one included) that there is a delay after either mon uses a charge move (shielded or otherwise) or whenever you or the opponent changes pokemon (be that faint or switch). This delay does NOT happen in the beginning, so the most important thing to do in any Rocket Leader battle is to lead with something that can tear though their shields without being shredded itself because they WILL use them first, every time. A second trick is to have your second mon be the actual fighter. For Sierra my gf’s first two mons are always Omastar w/ MS & RS and a machamp with his standard C/DP, didn’t even TM to CC or buy a second move (but he’s at least lvl 35). I eat Sierra’s shields with my first mon and with the delay of swapping to machamp (I also squeeze a MS in to charge just a little more before the switch) I lose much less health and destroy the first Lapras.
My final trick helps a lot in cases where you have to fight two of these buggers… Don’t charge your charge move to completion if you can farm a little more energy off of the last bit of health left after since there will be a delay. This is by far the trickiest because you have to know how hard your mon hits at various stages of its charge move being charged. That being said, I typically get 2-3 more punches in on the first Lappy, and whether I get a second Lapras or that Sharpedo I can get to DP before either can take out that Machamp. Throw a punch at her final mon as it comes out (delay) before switching to w/e I brought to fight it (another delay) and game over. Sometimes I have to bring Omastar or Machamp back which is why I always try to charge my mons just a little before switching them, that delay can let you rip off one last shot and I’ve had that be the match many times.
TL;DR Rocket Battles have delays between faints, switches, and charged move/shield use. Abuse this delay as often as possible (most easily with mons that have really quick charge moves).