How did Mega Sableye bypass Shadow Tag?

Question

I just had a gen 7 ubers battle. I was up against mega sableye and using mega gengar. I had switched into it to trap and finish it. But it switched out immediately on next turn! Please note I had already mega evolved before I switched into it (in an earlier part of battle)so please don't say ability doesn't activate in turn of mega evolution. Thanks in advance.

Answer 1

Generation VI
Ghost-type Pokémon are now immune to Shadow Tag.
Generation VI onwards
Ghost-type Pokémon are now immune to effects that prevent recall or escape (such as Mean Look and Shadow Tag), and they are also guaranteed to flee from any wild battle regardless of Speed.

Source

Since M-Sableye is ghost-type, it is immune to trapping.

Hope this helps!

Answer 2

The reason that Mega Sableye was able to switch out is because ghost types CANNOT be trapped.

As of Generation VI, Ghost-type Pokémon are immune to being trapped by all trapping moves and Abilities, including the binding effect of moves such as Infestation.

Source

Since Mega Sableye is part ghost type, it cannot be trapped.
Hope this helps.