Will these come to the asset?
Sorry for the rambling list.
Difficulty. The change the amount of health the enemies have. The amount of damage the enemy and dish out to the player per attack.Easy, medium and hard difficulty.
Fall damage.
Water volumes for swimming and possibly drowning.
And a surface to walk on that slowly damages the player. For example the toxic waste/lava surface in doom.
Flying enemies like a imp example.
And a flying enemy that has projectiles.
Turret enemy
quick save function.
Different hud overlay color specific for walking on a surface that hurts you or possibly other things that damage the player.
exploding barrels.
destructible items. Like for example you can shoot a bottle. Plays a sound effect and plays another flipbook animation that shows it braking. Or like a tv screen. Shoot it and it shows a cracked screen etc etc.
A item like a computer you press enter on or any object. And when you press the use button it plays a sound. Similar to the pinball table in dukenukem.
walking on a surface that triggers a large cube that can crush the player or something.Traps etc.
More weapons. Rocket launcher, BFG, Grenade weapon like the dynamite from blood or something like it.
A bow and arrow maybe that requires a buildup to shoot. For exameple it plays animation for a second then fires. Like the bow pulls back the arrow then fires.
The option for a weapon can cause a enemy to have a different death animation possibly like evaporate if they are killed by a specific weapon.
Level select.
Crouch ability.
settings menu for resolution, fulls screen, windows? The ability to remap buttons. Sound volume for music and sound effects.
When a enemy/boss dies triggers a door opening maybe. Or they can drop a key for a door maybe.
ladder
decals for bullet holes and explosions.
Once again sorry for the long list.