To make this more interesting, I'm only choosing films I've never seen before.

6 sequels:
The Exorcist III | Wes Craven's New Nightmare | Dawn of the Dead (1978) | Hellbound: Hellraiser II | Halloween III: Season of the Witch | The Texas Chainsaw Massacre 2

6 countries:
The Babadook (Australia) | Housebound (New Zealand) | Kill List (UK) | [REC] (Spain) | Let the Right One In (Sweden) | The Grudge (Japan)

6 decades:
The Green Inferno (10s) | 28 Days Later (00s) | Event Horizon (90s) | Lifeforce (80s) | The Hills Have Eyes (70s) | The Man Who Could Cheat Death (50s)

6 films before 1970:
The Invisible Man | Frankenstein | The Mummy | Creature from the Black Lagoon | Phantom of the Opera | Dracula

6 films from the following - Carpenter, Raimi, Whale, Browning, Craven, Holland:
In the Mouth of Madness (Carpenter) | Scream (Craven) | Drag Me to Hell (Raimi) | Bride of Frankenstein (Whale) | Child's Play (Holland) | Dracula (Browning)

3 people eating people (non-zombie):
Cannibal Holocaust | The Texas Chainsaw Massacre 2 | The Green Inferno

1 Hammer film:
The Man Who Could Cheat Death

1 Romero Dead film:
Dawn of the Dead

1 terrible oversight:
It Follows

2 Tobe Hooper films:
The Texas Chainsaw Massacre 2 | Lifeforce

Bonus:
It (1990) | It (2017)