For one year, Deathtouch was such a broken ability that Wizards of the Coast had to drastically alter it so that it could work as intended.

The ability has technically existed in some way, shape, or form since the game's 1993 debut, but it really didn't come into it's own until 2007 in Future Sight. The ability, which is sort of an insta-kill for creatures has since been used sparingly and has been tweaked through the years. But in 2010, Deathtouch was changed drastically.

Things got weird.

Deathtouch's rules were changed in Magic 2010 simply because, well, it became a big-time creature ability.

R&D had been somewhat put off guard by this however, and had only a short timeframe to work in Deathtouch. They kept the insta-kill ability, as well as the ability not being able to be used often. Players could double block and split damage now too, sort of as a way to balance it out. Blocking rules had been changed for 2010, too, so Deathtouch wouldn't get overly powerful.

But the reason why Deathtouch's new rules only lasted one year in 2010 was because of the unintended chaos.

First of all, Magic 2010 had a lot of negative feedback from players because, in WotC's attempt to simplify the game, the company wound up instead confusing players with new terminology and seemed to failed to adequaltely work in new abilities. This included Deathtouch. 

Magic R&D Director, Aaron Forsythe, said in an interview in 2011 that Deathtouch had been so rushed that they couldn't work in the new blocker abilities because of it. So that meant that Deathtouch, depending on the player, was blocked at every turn or became something as a prefered "nuke" in their arsenal.

As Magic had to wait a year to make the rule changes, any card with Deathtouch in 2010 suddenly became a hot commodity.

Finally, for Magic 2011, rules were once again worked around and Deathtouch was altered drastically once again. Damage assignment was changed dramatically and, since 2011, Deathtouch has only had smaller changes thanks to the R&D team figuring out the right changes for the game.

Today, Deathtouch is far less common an ability, but it is still very popular with players. It's a favored move, especially as a way to take out a hated creature or to provide that killing stroke. But it was once such a broken ability that it had to be altered after only a year.