Rosies are almost as infamous as the Bouncers in the BioShock series, mainly because they're the toughest enemies in the game and can easily kill you from a distance. While their straightforward attacks give them practically no weaknesses to exploit, it also means fights with them aren't particularly varied or unique. To change this, the Rosie needs to be more aware of its environment.
- Level 1: Rosie loot always holds rare U-Invent parts
- Level 2: +Damage
- Level 3: Master Trapster Gene Tonic (see here)
- Level 4: ++Damage
- Level 5: Arms Race Gene Tonic
A few things. Firstly, Rosies should be able to notice and shoot any explosives near you (Including the ones you're holding with Telekinesis). Secondly, Rosies could use Proximity Mines more intelligently. For example, if you take cover they can fire a Proxy Mine behind you, or set one as a trap on a door if you retreated through it. Other than that, there's nothing much that can be changed without altering the Rosie's toolset.
Since Elite Rosies are tougher and deadlier than their predecessors, they should also be able to use more advanced tactics. One one hand, they could be able to use Trap Rivets: they could try and lay them at your feet if you're running rowards them, or place them at walls and doors as traps. Also, you know the Big Daddy Bomb, the thing you throw with Telekinesis after sticking several Proximity Mines on it? Rosies could be able to make some of their own. Instead of piling up several Mines on something and then throwing it at you, though, they'll either pick up and throw an explosive at you, shooting it in mid-air; or grab it, slap on a Proximity Mine and fling it at you. Obviously, they'll be doing this with their hands, as they don't have Telekinesis, which means you get a small window of opportunity to shoot the explosive in their face. If you have the Plasmid you could even try and pull it out of the Rosie's hands and use it against him.
And that does the Rosie. Next up, the Rumbler!