I've been thinking if its possible or not, i haven't seen it done before and i had a good idea.

if i made a big empty box for a map with nothing in it and flat ground.
(tesxtures on the sky, walls and floor of course)

couldn't i create custom scenery tags for the terrain, vegitation, buildings etc
with health by creating model collision geometry tags?

how different is the model collision for bipeds/vehicles?

if i made a scenery model of a hill would the bipeds/vehicles be able to move around on it like bsp?

one more question, and thanks for the replies btw!

i edited the impact cyborg armor.effect from a few weapons
to spawn blood human burst.particle at negative incident and edited that tag to create bloodsplat.decal on collision.

the effect was great and i was wondering if theres a way to make blood decals stick to anything besides bsp? vehicles/scenery/bipeds?

The decals thing isn't even possible in halo 4. Decals have never rendered on non-BSP items, unless you use a piece of scenery that's very very close to a BSP plane (such as a billboard on a wall.)

At this point, some graphical glitch takes over and the decals appear on scenery if you are far away enough for it to render that way.