Originally posted by StronkWalrus:

Is it true that grass spawns mobs?
Read about it in a guide and just wondering if it is true or outdated

Spawns have different dynamics on how they spawn.

Obviously spawners like for draugr skels etc that you see visually are known spots that will spawn things.

Activities you do in different biomes spawn/attract mobs to you. Most of the time it is in a radius to you(similar to the event spawner radius).

And then there are the random spawning of biome appropriate mobs as you just move around(again with the radius mentioned), if you're lucky you can actually see them spawn in/render slightly off the ground and land for some.

Other factors:

Nigh time of course causes higher spawn rates.
Rain storms will spawn more necks in meadow biome.

Some subzone areas of biomes will have more propensities to spawn specific creatures(ie necks around water sources in meadows for example)

And there are others.

Also as partly mentioned, killing mobs then leaving render then coming back and cause respawns(sometimes seems on a timer too though). Note too that some areas (like in the meadows) can have a dynamic spawning area where different mobs have a rotation/random rotation of what spawns next in that rendering area.