Specific Entity Detector

I know Rei's Minimap posted here has forced entity detection, however I would like it to also show the name/icon of an entity nearby.
Basically, I'm trying to find a mod that can show me when a certain custom entity is nearby so that I can locate and capture it (its for Pixelmon, the Mew creature). However this may also be useful for other mods like this.

Why would someone make an extension of a mod just for another mod?