Pretty easy to get its health down and if you catch a Pokemon that can paralyze or put it to sleep it will make things easier... The problem is, it chews up your Poke Ball supply regardless of the kind of Ball you use. On my 2nd try (I killed it the first just to see what would happen if I did), 15 Great Balls I had with me, and I left with Victini and 4 Great Balls.