Do Pokemon’s Pokédex Entries only apply when it is not in battle?

Question

In HeartGold it says Tyranitar cannot be harmed by any attack, yet in battle it is harmed by enemy attacks.

Comments

Pokedex entries only ever apply in the anime, if they ever apply.

---

Of course not. Machamp can beat up Tyranitar and Tyranitar lost/ran to/from a bunch of Alolan Sandshrews in Pokémon Sun and Moon the series Season 2 episode 80.

---

Techinaically it waas battling the machamp and sandshrew

---

But it never battled Machamp, I just said Machamp can beat Tyranitar due to it's 4x weakness to Fighting types.

---

But According to HG pokedex antry it cant be harmed

Answer 1

The way video games behave depends on their machine code, and their machine code depends on their source code. Pokedex entries are not machine code or source code. Therefore, the way video games behave does not depend on Pokedex entries.
source