Focus Band does work on Shedinja, but there are some important details to consider. Shedinja is a unique Pokémon with a very specific ability called Wonder Guard. This ability makes it immune to any move that is not super effective against it.
Now, let’s talk about the mechanics of Focus Band. Normally, a Pokémon holding Focus Band has a 10% chance of surviving a move that would otherwise knock it out, leaving it with only 1 HP. However, this chance is only activated if the Pokémon is not at full HP. In other words, if a Pokémon is at full HP, Focus Band will not activate.
In the case of Shedinja, its HP is technically always full, as it only has 1 HP to begin with. So, under normal circumstances, Focus Band wouldn’t work on Shedinja because it is always at full HP.
However, there is an interesting interaction between Focus Band and Shedinja’s ability. Since Shedinja is immune to most moves, it will only take damage from super effective moves. If Shedinja is hit by a super effective move and the damage would normally knock it out, Focus Band can actually activate and give Shedinja a chance to survive with 1 HP.
For example, if a Fire-type move were to hit Shedinja, it would be super effective and normally knock it out. But if Shedinja is holding Focus Band and the chance activates, it can survive with 1 HP and potentially continue battling.
It’s important to note that this interaction only applies to super effective moves. If Shedinja is hit by a move that is not super effective, Focus Band will not activate, as Shedinja’s Wonder Guard ability will simply make it immune to the move.
Focus Band can work on Shedinja in certain situations where it is hit by a super effective move. However, in most battles, Shedinja’s Wonder Guard ability will protect it from taking any damage, rendering Focus Band ineffective.