The first Princess Shroob will be in a floating chair with a force feild around it. Whenever you do a lot of damage to the shield, it will change color. Blue-Green-Orange-Red-Dark Red and then the chair will cease function. THEN you'll be able to damage Princess Shroob. Princess Shroobs Chair has 2 attacks:
1. It will shoot lasers, then you'll either have to jump or stay put with either Mario or Luigi.
2. Tripod legs with grow out of it. It will walk until it's right above you, then shoot ring lasers around you.
You'll have to jump because the ring closes in on you, but don't jump too soon. Then the Tripod will bend in and land on you, so you'll have to hit it with a hammer. Princess Shroob herself has 3 attacks:
1. She'll shoot a fast moving energy ball at you. Jump. Might cause poisoning.
2. Shoot fast energy ball from above. Hit with hammer. Might cause poisoning
3. Shoots a wave of slow moving energy balls that will affect all characters. Might cause poisoning.
After you defeat her, you'll have to face a more powerful Princess Shroob (Her elder sister or something like that) She has A lot of Moves:
1. She'll realese a chain chomb following a ufo. Jump on it.
2. She'll charge at you. Nearly impossible to avoid, but you have to hit her with a hammer multiple times.
3. She'll throw a bing meteor rock at you. Hit Pincess Shroob with a hammer until she drops it.
4. Drinks Vim juice to heal herself 120 HP.
5. Jumps on UFOs. Will shoot fireballs at you from diagonally above, and to your side.
Then she'll turn into a tentacle beast. Don't attack her head. It'll only do 1 damage. First attack her legs, then you'll be able to attack her crown, so attack that, and when the Crown is greyish, THEN attack the head. It will do more damage. If her legs grow back, you can still do damage to her head, but if her crown lights back up, you'll do 1 damge again. Just keep doing that. Her attacks are:
1. Will swish around legs in a rotating fashion. Jump to avoid. She won't be able to do this without her legs.
2. Sharply "poke" Mario or Luigi. Jump to avoid. Could cause poisoning.
3. Shoot down helicopters. Hit them with a hammer. If electricity spouts out of them, they will hit Luigi. If fire, Mario.
4. Make a giant energy ball and throw it at you. If she adds more red fireballs than green, it will hit Mario, or green to target Luigi. Hit with hammer.
5. She'll creep up tentacles at you. Hit them with hammers multiple times so that she dosen't grab you and throw you.
Once you defeat her, you'll go back to the present. Then Bowser will become fused with Princess Shroob (I'm not telling you how). Bowser will attack you, and for every attack that you hit with a hammer or dodge, it will hit the spirit Princess Shroob and damage her. Keep doing this until her Shroob meter goes down. You can't attack or heal, unfortunatly, but it's still the easiest boss in the game. His attacks are:
1. Shoots multiple fire balls at you. If they go straight at you, jump over them. If they come from above, Hit them with a hammer. Knocks off 1/2 a shroob per fireball.
2. Shoots a HUGE fire ball. Hit with Hammer. Knocks off a Whole shroob from the bar.
Badges that REALLY help you are the Cure Badge A (Heals 10 HP per turn to wearer) and the Ulti Free Badge (Unlimited Bros. Items for wearer. Get at Fawful's Beans n' Badges (in the sewer place in a sewer pipe thing) for 90 beans.)
Check everywhere for beans. I also recomend you being AT LEAST level 29 for all characters (Or at least the adult ones, you only want the babies to use 1-up mushrooms and supers.) You want to have a lot of these items, too: Ultra mushrooms, Max Mushrooms, Ultra Drops, 1-UP Mushrooms, and UP supers.
And that's it. Good Luck with the Last 4 bosses!