They say that imitation is the sincerest form of flattery, and in this article I'm going to describe a simple but very effective tactic that I've shamelessly stolen from one of my local competitors - the topspin kick serve.
Before I get into the nitty-gritty of this tactic, I'll just point out that I'm not claiming that this serve would be a point-winner at the elite level of play, but at the level I compete at (around the WR 900-1200 or so), it's pretty darn effective.

I've seen the player in question use this serve time and time again against opponents of this level, and he has a very high percentage of success. After falling victim to this serve a number of times over the years, in recent weeks I've decided to turn the tables and try using the serve myself, with pleasing results.

Topspin Kick Serve - Simple Mechanics

Here's the bare bones description of the tactic - the server serves the ball with medium-fast speed and heavy topspin (the heavier the better, I've found), aiming to land the ball around two-thirds to three-quarters of the way up the opponent's court. The serve is kept as close to the height of the net as possible. Placement from side to side can vary, but into the playing elbow is always a good choice, with the wide forehand and wide backhand also being good options.

Topspin Kick Serve - Explanation

According to conventional table tennis wisdom, this type of serve is a no-no. It's not really a short double bounce serve, nor a fast long and deep serve, so it seems to give the opponent a golden opportunity to launch a powerful attack, right?

That's the main reason I resisted the urge to copy my competitor's serve in the past - I felt very vulnerable knowing I was deliberately going to serve the ball to what my years of experience tell me is the wrong location.
In practice, things don't work out that way, and now that I've bitten the bullet and tried this serve out for a few weeks, I think I'm starting to work out the reasons why. Here's my line of reasoning on why this serve works in the real world against sub-elite players.

• The linchpin of this whole service is the kicking effect achieved when the heavy topspin serve bites on the table at the opponent's side of the court. This effect kicks the ball forward and keeps it lower than normal. Everything revolves(!) around getting enough topspin on the ball to generate this kick.
• If the kick effect is achieved, then the ball will be likely to bounce lower than net height, and will jump forward off the bounce towards the receiver. Unless the ball is watched very closely, this results in a lot of mis-hits and even the occasional clean miss, since the ball is often a few inches lower than expected, and often several inches further forward than expected.
• By placing the bounce on the opponent's court in the two-thirds to three-quarters range, the ball is too long to flick with a wide angle, but short enough that the ball will be well below net height by the time it clears the endline. Add to this the fact that it has heavy topspin on the ball, making it jump off the opponent's racket as well, and it is a difficult ball to put away with a strong attack. I can personally attest to the number of times I've tried to power loop this serve, only to put the ball into the top of the net, or just miss the end of the table.
• By using a medium-fast speed instead of a very fast speed, the kick effect becomes more pronounced, while there is still enough speed to keep the opponent under pressure. If a very fast serve is used, the high forward speed already on the ball reduces the effect of the forward kick, since the kick doesn't add enough speed to the already fast moving ball. If a low forward speed was used, the opponent would have a little too much time to react and adjust to the forward kick. A medium-fast serve seems to give the right blend of pressure and kick effectiveness. You might need to experiment a little to find the best speed for your serve.
• I've tried adding some sidespin to the serve, but having to produce sidespin seems to reduce the amount of topspin I can generate, thus reducing the kick effect and overall effectiveness of the serve. In theory, if you could add sidespin while managing to maintain the amount of topspin you have on the ball, then some sidespin would be a plus. But I haven't been able to manage that myself.
• One final benefit is that it's hard to go too far wrong with this serve, provided you get enough topspin on the ball. If the serve goes a little higher, shorter or deeper than planned, it's still pretty effective, since the kick still makes it hard to punish well.

Conclusion

Overall, the use of this tactic has been a simple but effective addition to my arsenal of serves. There are just three provisos I'd like to make before I wrap things up:

1. Against truly elite players, this serve becomes much riskier since they are well trained enough to adjust to the kick effect and punish the serve regardless of how much topspin you put on the ball.
2. Be wary of overusing this serve, since a smart opponent will adjust quickly to the kick effect. It's a good serve to pull out in a pressure situation though, especially if you haven't used it before in the match.
3. Finally, remember that this serve is a gamble, although the odds are hopefully weighted in your favor. Any serve that bounces off the end of the table is inviting the opponent to attack it strongly, so be prepared! Now and again your opponent is going to get it right and hit his return past you for a winner, so don't get discouraged by the occasional failure - try to keep a rough count in your head of your successes vs failures, so you know whether you are getting a positive return when using this tactic.