Games with Halloween theme this year

Overwatch

Planetside 2 has the usual pumpkin hunt event.

Final Fantasy 14, if it's counts :-)

All games counts.

Lots of online games have a theme. And Terraria ofc :D

CS GO usually has chickens with pumpkin masks.

Rocket League
Dead by Daylight

elder scrolls online

If all games count - Simpsons Tapped Out on phone has a helloween theme event

World of Tanks console has a Halloween themed event. You can earn a Premium tank too.

TF2, maybe.

diamond city in fallout 4 celebrates halloween and christmas when the ingame date matches october 31st and december 24th =3

View attached image.

Dreadout

Payday 2 will have an Halloween update.
Just about every Artix Entertainment(AE) game will... it'll also have Thanksgiving and Christmas, the busiest months for AE are these three.
On top of that, the majority of there games let you play the past events alongside the new ones.