Bioshock > Splicers > Aggressor Types
There are five types of aggressor, each with a specific mode of attack. Each also gives different rewards from research. Certain types of aggressor are present, or absent, on certain levels; for example, there are no leadheads in Fort Frolic, nor are there nitros in Arcadia/Farmer's Market.
Thugs attack with hand-held weapons like pipes, wrenches, and machetes. They are your first opponents. Starting at Hephæstus, many of the thugs are electrified, sparking from off their clubs; such thugs are not only tough but are immune to electrical attacks, too.
Thugs have the habit of dragging their clubs along the ground, making a sparking sound. The noise of their electric arcs mark the electric thugs.
Researching thugs wins you the SportBoost tonics for greater speed and swinging force.
Leadheads attack with firearms, using pistols at first, but later graduating to machine guns. (For some reason, they do not use other types of projectile weapons like shotguns.) Leadheads keep their distance as they shoot you, but will use their weapons as clubs when up close. Leadheads are very tough to kill, taking a lot of punishment before going down. They make themselves vulnerable, however, when they stop to reload.
Leadheads make themselves known as they spin their gun barrels or pull their trigger bolts.
Research on leadheads yields first the Scounger tonic (rummage further through containers and dead enemies for different loot), then the upgrade to the Static Discharge tonic.
Nitros, also called grenadiers, carry the type of boom boxes you do not want to listen to: The kind that hold grenades (early levels) and Molotov cocktails (later levels), which they toss at you with amazing accuracy. Their only melée attack is throw a smoke bomb on the floor to distract you as they flee or maneuver into a better spot to attack. You can use Telekinesis to catch their bombs and toss them back at them, at other enemies or at obstructions.
The cans or bottles rattle inside their boxes, letting you know a nitro is in the area.
Research on nitros is specific to them: First, three in twenty bombs will likely be duds, then seven in twenty.
Spiders are the athletes of splicerkind. They can jump amazingly high into the air, crawl crab-style on ceilings, dash, leap, and do somersaults. And they hold a red-hot meat hook in each hand, with which they slash up close and throw like knives from far off (from floor or ceiling). You can snare their hooks with telekinesis and throw them back at them.
The sound of metal hooks biting into the ceiling and releasing chunks of it to the floor tells you that a spider is coming. On the ground, spiders swing their hooks back as they walk. The exceptions to this are the Sinclair Spirits splicers in Fort Frolic; these extremely aggressive spiders attack silently when they are not on the ceiling.
Research on spiders (your main mission at Port Neptune) gives you the ability to use their organs as first-aid kits. I said they were really healthy, right? Later, you get the highest-level Extra Nutrition tonic.
The Baby Jane splicer is emblematic of Bioshock; in the game's evil ending, an army of them slaughter the crew of a nuclear submarine.
When you see an aggressor walking around bare-handed, you got yourself a Houdini splicer. And they are not weaponless: They can shoot bolts of fire or ice from their hands, and they can teleport out of danger. If you hear a loud sucking sound, or see a blur or a blood-red or icy-blue cloud, a Houdini is coming your way.
Fire Houdinis are more common than ice throwers, who only appear in three levels. Their fire and ice bolts can be caught and tossed back with telekinesis, although a bolt does not have quite the bang of a bomb. You can also beat the bejesus out of them, as they appear to have no melée ability.
Houdinis make no sound at all as they walk. You tend to know they are there when you spot them first or when they cry out on seeing you.
Research on Houdinis wins you the most useful Natural Camouflage tonic. With further research you can more easily forecast where a Houdini will reappear: The blood/mist cloud is bigger and slower to coalesce, giving you more time to think up an attack or to hide.
Rapture is full of assorted mini-bosses on some of the levels. Visit the Special Aggressors page for more on them and their abilities.