Singed Passive Suggestion
Under Pressure Upon taking 400 -- 1800 damage withing 5 seconds (based on level) Singed's canister explodes into a poison cloud around himself, blinding enemies hit for 1 second. The cloud acts like Poison Trail and increases in size based on Singed's current Mana (120 second cooldown).
Additionally, he would get a small Health and Health Growth buff to make up for the loss of Tankiness. The "blind" is actually nearsight. So what Quinn and Graves have, not what Teemo has.
Edit: And the cloud could range from everything from a small cloud with low Mana to a Doom Bot Blitz Ult if he builds 6 Seraph's Embraces. The sound effects would then match the size.