Here is a little exploit that work on the most private server, or. It is a bug, well whatever.
It is the talent "Combustion" that mages gets in their fire tree on level 40, this spell is kinda bugged and procs so you get 100% crit chance with fire spells.
And it is so simple to do;
1. Activate Combustion.
2. Now you'll see the buff upp in the buff corner.
3. Start shooting fire spells against a enemy until it is a "10" mark on the buff.
4. Have fun with 100% crit chance.
This isnt maybe a new bug, but it is a great one.
Enjoy.