Trapper - This class was released among with its Tier 4 upgrades July 18th, 2016. It shoots concave hexagons with three-fold rotation symmetry, called traps, that become stationary after having traveled a short distance. These traps are harder to destroy than other bullets except for the Destroyer's and Hybrid's. After a certain amount of time they disappear. The traps can severely damage enemies if they run into them. (If you constantly get mixed up in FFA aka Free For All, remember that the traps have curves in them.)
Build a wall: One of the most well known strategies/tactics for all trapper classes:
Start to shoot traps/mines out on front of you to make a circle (or enough for you to put yourself in) and get inside it. It's called "The Base".
Shoot traps/mines in the direction you want, try to spray up and down rapidly in until it looks like an arc. It's called "The Wall".
Finally, the "Wall" is made and can protect you from incoming bullets at the opposite side of the wall. If you get flanked from behind, you just simply walk to the other side of the wall.
Note that you can push the wall by creeping slowly while maintaining the wall by shooting traps/mines into it.
Snipers: Most snipers are good counters to Trappers. They fire at a nearly equal rate and make your traps dissipate as fast as you can create new ones. Unless you see they are pretty bad at being a Sniper, run off.