Battletoads/Double Dragon was the fourth game in the series, and a crossover with the Double Dragon series developed by Technos Japan. It was released for the NES, with ports for the Super NES, Sega Genesis, and Nintendo Game Boy. Despite the presence of the Double Dragon characters, Technos Japan had no actual role in the game's development.
Reports of an unidentified flying object in space lead to a shocking discovery: The Dark Queen has invaded Earth with an all-new battleship, the Colossus. To make matters worse, she has allied her own forces with the Shadow Warriors, a gang of human criminals who also desire world conquest.
Feeling a bit overwhelmed, the Battletoads get into contact with the Shadow Warriors' archenemies: Billy and Jimmy Lee, the Double Dragons. The Ultimate Team assembled, they take the Battlecopter up to the Colossus and begin to battle the evil alliance.
Battletoads and Double Dragon is the first game in the series where all three Battletoads are playable. In addition, Billy and Jimmy Lee are playable characters. Though the five characters have slight differences in performance, in general the 'Toads have slower, but more powerful Smash Hits, whereas the Dragons use Dragon Techniques that react faster but aren't as damaging.
Compared to prior Battletoads games, vehicle stages are kept at a minimum. There are only two such areas: one being a Turbo Tunnel-like hallway in Stage 2, and the other a space shoot-'em-up in the vein of the classic video game Asteroids. The meat of the game lies in platforming and fighting enemies, though the stages do present significant challenge.
Stage 1: Tail of the Ratship - The battle begins on the literal tail of the Colossus. Shadow Marines and Retro-Blasters make up the bulk of the defenses, and Mechano-Mitts pack a punch. If all else fails, Abobo stands by to crush all intruders.
Stage 2: Blag Alley - As the 'Toads and Dragons progress into the hallways, they'll need to keep on their toes against Guidos and Walkers. Toss the Doormen of Doom's TNT back at them to proceed, and don't lose your ride during the Turbo Tunnel area. Big Blag is the boss.
Stage 3: Ropes and Roper - Things are more intense in Stage 3. Linda Lash's attack in force and the pounding pistons can make pancakes out of 'Toads and Dragons alike. When rappelling, avoid the electric fences and kick the birds off the walls to survive. Don't let Roper open fire on you.
Stage 4: Ratship Rumble - In this stage, you're flying a space pod and are tasked with shooting everything that moves in order to survive. You have two weapons: a rapid-fire gun and a homing missile, though you'll need to manually lock onto a target in order to use it. The last enemy is the Colossus itself.
Stage 5: Missile Mayhem - The Colossus managed to fire off a very large missile at Earth. The 'Toads and Dragons must ride the missile and fight to the front. Enemies include Rats, Lopars, and repeated encounters with General Slaughter. The missile itself is piloted by Robo-Manus.
Stage 6: Shadow Boss Showdown - The missile's no longer a threat, but the Shadow Boss has escaped into a basement warehouse. It's a short hike through more Guidos and Walkers to the Boss, and he knows how to throw his weight around.
Stage 7: Armageddon II - The Rematch - You've finally cornered the Dark Queen! Defeat the last few enemies and beware her fiery powers.