How often have you played somebody with, for lack of a better word, weird shots? Perhaps they hit shots with a floppy wrist (so you could never tell where the shot was going), or with sidespin on shots that normally don't have sidespin, or perhaps they just used a non-inverted surface that you weren't used to seeing. There are infinite possibilities. The problem was that you found these "weird" shots difficult to play against with your more fundamental game. Why does one with sounder fundamentals have problems with weirder games, and how can you overcome that?
There's nothing wrong with having a little weird in your game to throw opponents off. But there's a reason why certain shots, mostly done with inverted rubber, are done by the top players, and are considered orthodox play. Learn these fundamentals, and you'll have an advantage over those who have not mastered these fundamentals. This doesn't mean you'll win, but a player with weaker fundamentals will have to essentially play at a higher level just to match you. For example, to use the floppy wrist example mentioned above, the timing needed for such shots is much higher than for more orthodox technique, and so that player will always be handicapped by this. But this is often offset by the inherent "weirdness" of the shot, since you aren't used to it. How do you overcome this?
The keys are depth and consistency. Against any type of weird shot, if you keep the ball deep on the table, you'll have more time to react to the less orthodox shots coming back at you. Given time, your better technique should beat the weaker technique, unless the other player is simply better. Given the time needed, your more orthodox shots should be more consistent at any given pace than the less orthodox version.
It's not always this simple. For example, depth may give you more time to react to the opponent's shot, but it also gives him time to attack, especially by looping. So against a looping opponent with unorthodox technique, you might start by going short, or perhaps long to a spot where he can't loop (often deep to wide backhand), or simply find ways to attack first (deep on the table), and then turn it into a more even battle of good versus "bad" technique. Or against a non-inverted surface, where it's the surface that's "weird," not the technique, you would need to understand the properties of that surface so you can play against it properly - but again, depth will give you more time to react to it.
There has always been an age-old battle of standard versus non-standard technique. Sometimes the non-standard technique becomes standard, such as reverse penhold backhand, the banana flip and other backhand flips (often done against balls that are short to the forehand, once considered a no-no), or even looping itself (which was a "weird" shot until it became more common in the 1960s). And sometimes a player with "good" technique has something different to throw at opponents, such as the grip change to a very forehand grip Timo Boll often does when looping to get an extreme and "weird" inside-out forehand loop.
But good technique (i.e. sound fundamentals) almost always wins out against the less sound ones, so you should master these fundamentals. It's often after players have mastered these fundamentals that they experiment with other ways, and sometimes find something to do that is "different." (Here's a related article I wrote on this, "Develop the Fundamentals: Strokes and Footwork.")