It’s cleaning time in Pokemon GO. Not a physical cleaning, mind you, as that would be an unusual type of in-game event, to say the least. We’re talking about the kind of digital housecleaning that the developers go through to prepare for a big new content release, which is exactly what fans expect when Gen 4 Pokemon hit the game soon.

(When, exactly? Niantic hasn’t revealed that information just yet, but the best guess is that the new Pokemon are coming before the end of October.)

To get ready for new characters, the devs have taken a hard look at the stats for the hundreds of Pokemon already in the game. As the always intrepid people at The Sliph Road have discovered, almost every character in Pokemon GO has been part of a massive rebalancing that has led to lower Defense stat values for the majority of Pokemon, along with buffs in other areas. The end result is that some of the best defenders have been nerfed a bit, though they should still be good for defending gyms even if they are slightly less effective.

In all, 13 Pokemon have been nerfed, meaning their CP values will drop once the rebalancing changes, which have been temporarily rolled back at the time of this article, are put back in the game. Here’s a quick look at who’s been hit the hardest in the relative order of how much the nerf affects them.

Pokemon Whose CP Values Will Drop

  • Blissey
  • Chansey
  • Snorlax
  • Rhydon
  • Slaking
  • Vaporeon
  • Relicanth
  • Rhyhorn
  • Ho-Oh
  • Steelix
  • Noctowl
  • Donphan
  • Aggron

Note that at the bottom of the list, the reduction in CP should be very minor, where the effects on the likes of Blissey, Chansey and Snorlax will be more profound.

That means every other character in Pokemon GO has been buffed in terms of overall CP, though in most cases their defense stats will still see a reduction (about 75 percent of Pokemon will see defense nerfs). We’re obviously not going to list all 300-plus Pokemon to be buffed, but here’s a list of the top 25 beneficiaries of CP buffs.

Top Pokemon Whose CP Values Will Rise

  • Deoxys
  • Shedinja
  • Alolan Dugtrio
  • Starmie
  • Magnemite
  • Gengar
  • Dusclops
  • Hitmontop
  • Magneton
  • Haunter
  • Absol
  • Mr. Mime
  • Scyther
  • Hitmonchan
  • Staryu
  • Gastly
  • Banette
  • Dugtrio
  • Dodrio
  • Alolan Diglett
  • Breloom
  • Anorith
  • Kingdra
  • Blaziken
  • Salamence

When will the changes be reinstated? We don’t know for sure, but depending on when you read this article, it may have already taken place. The idea is to level the playing field a bit to make sure that everything is perfectly balanced (h/t Thanos for that phrasing) for when the Gen 4 Pokemon arrive. While not all of them will enter Pokemon GO at the same time, we’re talking about 107 new pocket monsters when it’s all said and done.

Again, the CP changes don’t mean that workhorses like Blissey and Snorlax won’t still be great gym defenders. They just won’t be quite as superior compared to some other options, and that should be a good thing in the long run.

Looking for more Pokemon Go guides? Take a look at our tips on what to expect from 7 km eggs and our trading guide, for starters.