Putricide brings a lot of utility, and due to his low damage output, he shines the most when with a partner. Be careful when alone, for even though some of his basic abilities have multiple stacks, they have very long cooldowns, and is nearly useless without any of them.
Festering Gas is his main form of damage, offering not only an okay form of lane clearing, but a utility for weakening enemy heroes. Use it to deal with pesky assassins or to discourage them from entering a fight where they would be at a disadvantage.
Rotting Slime is a tricky weapon in the lane, but creates a dilemma for an enemy hero unfortunate enough to be fixated on. When chasing Putricide or an ally hero, they will be forced to choose whether to focus their attention on killing the ooze, or finish the chase knowing they are pestered by the damage and slow. Alternatively, when being chased, they may risk killing the ooze while under attack, or try and escape with enemy heroes narrowing in. Any fight is a risk to the enemy when pestered by an ooze.
The
Choking Gas is Putricide's mane form of escape and spell disruption. If not even the ooze can slow a mobile enemy enough, use the choking gas to briefly stop their movements. Even half a second can be enough to save you from certain death. This may also give you a chance for a well timed Rotting Ooze. But be very careful. A poorly fire throw can leave your ally hero vulnerable to a quick thinking enemy, and be punished even quicker from your mistake.
Don't forget that each ability used will provide stacks for your
Healing Gas. Assuming no auto-attacks are used, every 4th ability will heal nearby heroes for a decent amount. Be sure to time your positioning and abilities well, or your next healing may not be used to its full potential.
Even a weak support likes damage, and
Putride Mutation can provide a lot of it. Turning a low damage support into a temporary tankish assassin. With the added attack speed, you are even able to add stacks for healing gas at an increased rate. The addition of the leap will also apply for a useful engage or an emergency escape.
Don't care for damage and want more disruption? Then go for
Pepto Abyssmal. This may require you to get up close to an enemy, but it will force them think quick unexpectedly. In addition to basically stunning them after a 2 second delay, this can cause an enemy to deal damage on their own team, forcing them to quickly reposition away from their allies, or leave themselves vulnerable, all while taking damage.
I would suggest a far lower CD on Choking Gas tho :D