I've had this sitting around for a while.
In short, Corrosion will be a subtype of the Poison status that burns the internals of the enemy, turning them into living bombs. The status itself does not affect the enemy, but upon death, corroded enemies will detonate, causing damage proportional to the monster's health in a 1 block radius. Since this is derived from poison, it does not affect poison element enemies.
Corrosion, like curse, will be administered in a limited fashion, in a branch off of the Toxic Vaporizer series.
Corrosive Canister (4*)
Flavor text: A Toxic Vaporizer that holds a small amount of highly concentrated, experimental gas that corrodes the organs of the enemy. Knights are warned not to tamper with the canister, but some have managed to weaponize it.
This bomb retains the radius of the three star Vaporizer, and imparts Good Chance to cause Moderate Corrosion. Damage caused by enemy detonation is equivalent to 70% of the corroded enemy's health. In addition, the bomb charges slightly linger (5000 millisecond charge time) and slows you down like the Vortex.
Corrosive Eruption (5*)
Flavor text: A potent bomb brimming with acidic fumes. It smells slightly of almonds.
Same stats as 4*, but instead has Good Chance to cause Strong Corrosion. Damage caused by enemy detonation is now equivalent to 100% of the monster's health.
Discuss.
Before introducing a new status in a weapon, introduce the status; according to your description it turns the defeated enemy into an explosion which deals damage "proportional" to its health; does this mean its total health is the damage inflicted? Although it only affects enemies in a single space radius that does not balance the amount of damage it does. Kill one, get at least one other kill free; if the damage on death is even half of the health of the enemy it is an overpowered status.
Think of T3 where everything has ~1k+ health each. Now imagine a Vaporizer bomb which goes to 5* and is used in an arena for the last wave of the last room or a Slag filled room in Firestorm Citadel where everything is clumped together. The idea of "corrosion" causing the defeated enemy to explode promotes teamwork by having the user work with someone who is killing everything, but the damage is far too high.
"Corrosion" sounds more like poison and fire combined; consider changing the term to something more relevant to its mechanic such as "infected", "tagged", et cetera. Curse is limited to vials and Faust line. Making a Vaporizer for a status as powerful as curse would be far too overpowered.