Incinerate! is one of the only plasmids capable of killing enemies entirely on its own. It is a pure damage-dealing plasmid, meant to kill as many people as possible. The upgrades I came up with are designed to make the plasmid more "contagious", i.e spread from enemy to enemy.
Incinerate! 2 Upgrade #1: Fire Bomb. The equivalent to BioShock 2's Incinerate! 2. Charging up the plasmid allows the player to cast an improved fire blast, able to ignite multiple enemies. Unlocks Incinerate! 3 upgrades #1 and #2.
Incinerate! 2 Upgrade #2: Panic! Splicers hit by the plasmid will run in fear towards other enemies, setting them on fire. Unlocks Incinerate! 3 upgrades #3 and #4.
Incinerate! 3 Upgrade #1: Flamethrower. Just what it says on the tin. Burn enemies with a continuous stream of fire from your hand! In addition, a simple plasmid cast is equal to a fully-charged Fire Bomb. The flamethrower effect deals much more damage than in BioShock 2.
Incinerate! 3 Upgrade #2: Inferno. A simple cast is now equivalent to a fully-charged Fire Bomb. Charging up the plasmid spawns a miniature sun which randomly ignites all nearby enemies for a set amount of time before disappearing, allowing the player to use other plasmids and weapons in the meantime.
Incinerate! 3 Upgrade #3: Fearful Flame. Splicers set on fire by a panicked enemy will also run in panic, making for room-clearing chain reactions!
Incinerate! 3 Upgrade #4: Fireworks! Panicked Splicers leave a trail of fire behind them, igniting anyone who passes over it, and will spew out flaming projectiles at random as they run.
Again, feel free to post your opinion on my ideas.