You can't really increase the range you can see entities themselves, but you can create particles at their location. Put the following command in a repeating command block:
/execute @e[r=50] ~ ~ ~ particle <particle name> ~ ~1 ~ 0.1 0.1 0.1 0.1 1 force
I can only see mods/players for 20 blocks, can I increase this, any way is helpful.
If you mean changing the distance in which a mob can track you, you can use the entitydata command to change a mobs' attributes.
/entitydata @e[type=Skeleton] {Attributes:[{Name:generic.followRange,Base:100}]}
Check it out here!
You can't really increase the range you can see entities themselves, but you can create particles at their location. Put the following command in a repeating command block:
/execute @e[r=50] ~ ~ ~ particle <particle name> ~ ~1 ~ 0.1 0.1 0.1 0.1 1 force