Plant Man is a Robot Master with a straightforward stage in the 'Forgotten Area' of a rainforest. While the latter parts can present a challenge, Plant Man himself is easy, and the Rush Jet Adaptor is obtained from him. Springs and grass are the stage's main gimmicks. Springs in this stage are yellow and allow Mega Man to bounce higher when holding the jump button. Grass acts as cover, obscuring enemies and Mega Man's legs alike.
The beginning of the stage is a horizontal outdoors section. Two Heli Butons will ambush you by emerging from the trees to deal three points of damage on contact. They have two health points each, so any weapon can be used. Beyond them lies grass with a Batabattan. Their jumps can be slid under, but the window is relatively tight. They are destroyed in one hit, shoot them with the Mega Buster while they jump. Two more lie ahead on higher platforms, along with a block that can only be broken by the Rush Power Adaptor. Your reward will be a large health capsule and an extra life.
Jump up to the ladder and climb up. You will enter a room with a Power Slam. It has twelve health points, and attacks by thrusting diagonally up until it is above you, at which point it will power-slam downward. Come into the room with a charged Mega Buster shot, slide under it when it first comes down and fire, jump up to the higher platform, slide under its second slam. Then take it out. Beat destroys it in one hit, but otherwise use Flame Blast or rapid-fire Mega Buster shots.
The next section has some Tadahou and Propeller Eyes. The Tadahous are cannons with three health points that shoot directly forward. The Propeller Eyes only move when vulnerable, and also have three health points. Just shoot them with charged Mega Buster shots. Drop through the gap at the end of the room to get stuff from Eddie.
Below that, you'll encounter the first of two Gorilla Tanks. (that is to say, robot apes on tank treads.) This guy is vulnerable in the head, so shoot him there with Flame Blast if you have it. Keep shooting him below the head if he is not attacking, so you won't be cornered and easily hit by his bullet spread.
The following section is filled with Heli Butons and Batabattans, obscuring grass included. At the end of this, there is another block that can only be broken by the Rush Power Adaptor. Break it, and you'll net yourself two large energy capsules. Afterward is the second Gorilla Tank; employ the same tactics to defeat this one.
Near the end of the stage, you'll have to traverse a spring-filled marshland with plenty of instant death situations. Dodge the robots that try to push you to your fate, returning fire when you can. Watch out for the Jet Butons, who can knock you out of the air into the watery pits - The first of which charges as soon as you pass the first two springs! The Gabgyo fish pop out of certain water pits, so stay close to the edge to lure them out and shoot them before jumping over. You can use the springs to jump up high over the Jet Butons
Alongside those, you'll find a few more Tadahou and some platforms that open when you shoot at their flashing core. Those flashing flower cores at the top of the screen are actually energy pellets, so jump up and grab some! The water pits get wider here, so be careful. Two Tadahous are on springs themselves and will fire at different elevations, which means you'll need to use a charged shot as soon as they appear. One more Tadahou lies before the boss doors.
Plant Man is not a hard boss. His patterns are very similar to those of Star Man, and he's even easier. He'll put on his shield, do a jump, and throw the shield at you and run forward, repeating this for the entire battle. He's only vulnerable when he's without the shield, so when he throws it, jump over and either use charged Mega Buster shots if this is your first stage, or stop him with extreme cold from the Blizzard Attack.
Victory gets you Plant Barrier, and the Rush Jet Adaptor.