One of the core mechanics of the Pokemon franchise is how effective your Pokemon's type is against your opponent. For instance, a Water-Type Pokemon is strong against Fire-Type Pokemon but weak against Grass-Type Pokemon. When a Pokemon has two types, some attacks become even more powerful or weak.
Pokemon Go's version of this mechanic was a bit more nuanced. In the core game, a "super effective" attack would do twice as much damage, but players only got a 1.25x boost in Pokemon Go. This meant that some Pokemon (like Gyarados or Rhydon) were much more viable as gym defenders because "super effective" attacks did a lot less damage than they should. At least, that's how it used to work.
Pokemon Go just updated its GAME MASTER file, which (among other things) basically tells the game how much damage attacks are supposed to do. Players have discovered that all of the attack bonuses have changed, making type effectiveness even more important than before.
Keep on scrolling to see exactly what changes were made and how they'll impact battles in Pokemon Go moving forward.
The biggest change is to the "super effective" bonus. Originally, a Pokemon would get a 1.25x bonus when they hit an opponent with an attack they were weak to. So, a Thunder attack would do 125 damage to a Squirtle, while it would only do 100 damage to a Rattata.
With the new changes, the "super effective" attack bonus now does 1.4x as much damage as a neutral attack, as opposed to 1.25x as before.
What's more, a "double super effective" attack will get a 1.96x boost compared to the 1.5625x boost from before. This means that Pokemon like Gyarados and Rhydon will suddenly be a lot less effective as a gym defender than before.
To make up for the super effective boost, the same type attack bonus (STAB) has been nerfed slightly. Pokemon get STAB when they use an attack that has the same type as their species. So, a Pikachu using a Electric-Type attack gets STAB, but a Pikachu using a Normal-Type attack does not.
The STAB bonus used to be a 1.25x bonus, but now it's only a 1.2x bonus. This means that Pokemon who have attacks with different types won't be quite as useless in gym battles.
The reduced STAB bonus means that super effective attacks are even more powerful than before. Originally, a Pokemon who does a super effective attack with STAB would get a net 1.56x bonus. Now, a super effective attack with STAB will get a 1.68x bonus. More importantly, a double super effective attack with STAB will get a whopping 2.352x bonus.
Basically, Pokemon with two types are about to feel the hurt in gym battles.
Pokemon Go has also changed how resistance to attacks work. Originally, Pokemon would do only 80% their usual damage if they attacked a Pokemon with a "not effective" attack. So, a Thunder attack would only do 80 damage to a Sandshrew (a Ground-Type) instead of the usual 100 damage.
With the new changes, a non-effective attacks now only do 0.714x as much damage than they do usually.
More importantly, a second tier of resistance has been added to Pokemon Go. In the core games, some Pokemon are wholly immune to damage from certain types of attacks. A Ghost-Type Pokemon, for instance, can't be hurt at all by a Normal-Type attack.
In Pokemon Go, resistance and immunity were originally counted as the same. However, Pokemon will suffer only half the damage if they're immune to a certain type of attack. So, a Normal attack with a base damage of 100 would only do 50 damage to Gengar (a Ghost-Type) instead of 80 damage.
It's very possible that other changes are still in store for Pokemon Go's attack and defense stats. There's a very good chance that we'll see a rebalance of some kind to nerf how much damage certain moves do to offset these big changes.
It's also possible that Pokemon Go will change the core formula to how damage is calculated, so that a Pokemon's base Attack and Defense stats are even more important than before.
Even if these are the only changes Pokemon Go makes, it's clear that the new gym system is going to really shake up the metagame and gym battles.
More Pokemon: First Look at Pokemon Go's New Items / Pokemon Go Fest Tickets Sell Out in Thirty Minutes / Here's How Pokemon Go Will Add Legendary Pokemon / Pokemon Game Confirmed in Development for Nintendo Switch / Pokemon Go Teases Plans for Exciting New Playground Feature / More New Features Teased for Pokemon Go / Pokemon Ultra Sun and Ultra Moon Announced / Legendary Pokemon and More Confirmed for Pokemon Go This Summer