Ruling Rising rivals kecleon

[J-chan lll]

http://www.pokebeach.com/tcg/rising-rivals/scans

I need to know, what is the purpose of its ability? how is it helpful?

 

[DNA]

It lets it hit for Weakness (as well as Resistance) on any Pokemon. It also gets support for type-specific cards, like Sunyshore City Gym (which lets it ignore resistance and erases weakness) and Shaymin LV.X's Thankfulness.
Oh yes, and it gets the bonuses from Special Dark and Special Metal energy.

It gets support from almost everything. That's the purpose of its Poke-Body.