use a poke-ball on it
The same way you would catch a normal Pokemon. The only difference is is that the Pokemon is shiny.
use a master ball
Explore!
in some cave
The easiest way is just buy a r4.
Using a Master Ball.
fishing in the safari zone is the easiest way.
use a masterball
the easiest way to catch a roming Pokemon is to get lots of ultra balls and a Pokemon with mean look use mean look on it weaken it and start throwing the utra balls.
The easiest way is to catch a Timburr and teach it Rock Smash.
If you havn't used you marster ball yet use it
put honey on a tree and wait for 6 to 10 hours. or the easiest way is to catch it in eterna forest