Contagion

The Contagion is a mobile-exclusive LMG added to  in the 1.9 update. It costs $9.99. Although it is a weapon, it doesn't have DoT but instead explosive shots with small radius.

Contrary to what the description says, the Contagion packs more than a punch than other LMGS. Its crowd control potential is immense in early game, with enough dps to be a fantastic bossing weapon for low levels.

One more advantage is that this weapon don't require level condition. So you can buy this once and you can have new characters use it. It's really useful if you play Zombie Hotspot Contract as you can maul down a lot of zombie in just 2 minutes. It works best on the Uranium mine map.