as example

The Controller is a green Flying Parasite that controls one of four characters: Marco, Tarma, Eri, and Fio. Attacking the possessed host will destroy the Controller. When the Controller is destroyed, the character gets up but sits down exhausted, and a SV-001 Type-R drops from the ceiling. In the ending of Morden saving the player character(s), the possessed character is seen in a Mini-UFO.

The Controller's host is the character who was seen falling in the final mission's cutscene, which depends on the characters that Players One and Two were controlling at end of mission 4. The host becomes unselectable for the entire mission.

Player 1 Host Unless Host is P2
Marco/Ralf Fio Tarma
Tarma/Clark Eri Marco
Fio Marco Tarma
Eri Tarma Marco

The Controller's host's attacks include having the host alternatively fire a Heavy Machine Gun while spinning around like a ball, a standard Rocket Launcher, and a green Flame Shot. When close, the host uses their melee attack (hatchet/knife). Sometimes, they'll throw a grenade or fire a small shot of their pistol.

Metal Slug Tetsuyuki | Hairbuster Riberts | Tani Oh | Shoe & Karn | Iron Nokana | Hi-Do

Mini-Bata | Allen O'Neil

Metal Slug 2/X The Keesi II / Iron Nokana MK II (X) | Aeshi Nero | Dragon Nosuke | Big Shiee | Hozmi | Rugname

Mosque Artillery | The Keesi II (X) | Allen O'Neil | Dai-Manji

Metal Slug 3 Huge Hermit | The Ten Commandments of Moses | Jupiter King | Sol Dae Rokker | Rootmars

Twin Ohumein-Conga | Monoeyes | Hairbuster Riberts | Hi-Do | Rugname

Metal Slug 4 Brave Guerrier | Toschka Dalanue | The Iron | Big John | Sea Satan | Amadeus Mother Computer

Mecha Allen O'Neil

Metal Slug 5 Metal Rear | Shooting Ray | Wall Crawler | Sandmarine | Evil Spirit Incarnate

Black Hound | Stone Turtle (unused) | Mammoth Tower | Ptolemaios (unused)

Metal Slug 6 Bull Drill | Iron Sentinel | Brain Robot | Sea Worm | Invader Queen

Invader Controller

Metal Slug 7/XX Worm Mecha | Crablops | Destroyed Crablops | Fall Mecha | The Union | Rebel Gigant | Kraken
Metal Slug: 1st Mission Rebel VTOL | Rebel Train | Macba | Rebel Zeppelin | Eletromagnetic Crane | Weapons Port Boss | Hilde Garn

Facility Elevator | Macba | Rebel Truck

Metal Slug: 2nd Mission Big Bertha | Terrain Carrier | Rebel Reactor | Macba | Rebel Submarine | Tani Oh | Gunslinger | Rebel Submarine | Rebel Airplane | Hilde Garn's Slug | Rocket UFO

Rebel Rocket | Hyakutaro

Metal Slug Advance Formor | Emain Macha | Kaladgolg | The Keesi III | Cabracan

Allen Jr.

Metal Slug 3D M-3 Rocket Van | Mosque Artillery | Spider-Bot | Rebel Underground Drill | Big Shiee | Morden Castle | Allen O'Neil | Lugus | Lieu Monster
Mobile games Rocket Control Room | Unknown Alien | Hellfire | Spiderbot | Cyclops | Mega Laser Turret | Mars Battle UFO | M-32 Water Carrier Plane | Mecha Kaiju | Alien Floating Structure