Banes Trait is pretty simple:
No activation time, can be done at any time. Pressing trait gives you one level of venom up to 3. For each level you do % more damage and have 1 hit of armor/projectile stopping on your specials. Not normals.
Each level adds to the speed of venom draining.
After venom is gone, Bane is weaker/slower/takes more damage, depending on how much he used.
Haven't played as him so can't judge, but judging by his frame data, hes slow as hell, and doesn't have many ways to get in, outside his charge move with armor.
Doesn't look high tier from his data to me. His anti air has 4 different outcomes, depending on how you catch them.