well, if you're trying to catch it the first time you meet it (trying to get a good nature/IVs, etc.), then it can be a bit irritating, because you don't have the MBall yet. however, it's not that tough. my usual team at that point in the game is espeon, typhlosion, amphy, and random irrelevant stuff. espeon sweeps away delcatty and bannette away, and typhlosion deals with steelix and vileplume in one hit each. after that, just flame wheel suicune to the yellow, and have espeon put up a Reflect and typhlosion a Sunny Day. send out ampharos to t-wave and light screen, keep using the ball-switching trick with Net Balls (which you can buy at the outskirt stand for 1000, if you already used the one you should've found in the overworld).
it took a while, but i rather like my bold CMCune...