Viper as of writing this has 2 passive abilities:
FUEL - which drains while using poison cloud or toxic screen (having both of them activated makes the fuel drain 50% faster).
TOXIN - abilities that apply Toxin cause affected enemies to have their maximum health instantly decayed, which then gets lower the longer they stay within the ability's area of effect.

Her basic abilities consist of:
SNAKE BITE - equips a chemical launcher. Fire to launch a canister that shatters upon hitting the floor, creating a lingering chemical zone that damages and applies Vulnerable.
POISON CLOUD - equips a gas emitter. FIRE to throw the emitter that perpetually remains throughout the round. ALT FIRE to lob. RE-USE the ability to create a toxic gas cloud at the cost of fuel. This ability can be RE-USED more than once and can be picked up to be REDEPLOYED.

TOXIC SCREEN is her signature ability, which equips a gas emitter launcher. FIRE to deploy a long line of gas emitters. RE-USE the ability to create a tall wall of toxic gas at the cost of fuel. This ability can be RE-USED more than once.

VIPER'S PIT, which is her ultimate equips a chemical sprayer. FIRE to spray a chemical cloud in all directions around Viper, creating a large cloud that reduces the vision range of players and maximum health of enemies inside of it. HOLD the ability key to disperse the cloud early.