Strider

Natural spawns for the Strider occur in Nether (lava oceans).

That single-biome restriction means Nether (lava oceans) is the only place to look; if you are not there, you will not find one, so locating the biome is the real task.

Spawns on lava surfaces in the Nether in groups of 2-4.

Being a Nether mob, it ignores the Overworld's darkness rules and can spawn regardless of light level within its home biomes, which makes the Nether dangerous even in well-lit areas.

They tend to arrive in clusters of 2-4 rather than alone, so expect to meet more than one at a time.

Remember that this is the Nether-only — you will never run into one back in the Overworld under normal conditions.

With no attack to worry about, the Strider is something you gather or farm rather than fight.

Killing a Strider produces the following loot:

Every kill yields 2–5 String (always, 100% chance).

You also collect 1–3 experience for every Strider you defeat.

String from striders is renewable, so a small breeding setup keeps you supplied indefinitely.

Since every item here is guaranteed, the only variable is quantity, which makes this mob a dependable, low-variance source of what it carries.

Because the Strider is harmless and breeds, the efficient long-term approach is a small enclosed pen where a breeding pair keeps replacing what you harvest, rather than hunting wild ones down one by one.