Enemies are littered throughout every level of the game and will hurt Mario when they hit him. The standard way to attack enemies is to stomp on them, but do not jump on anything with spikes! You can also throw shells at them or become Fire Mario and throw fireballs, though fireballs will not hurt some enemies.
- Goomba: One of the most common enemies in the game, the Goomba is also the easiest enemy to defeat. One bounce will dispatch this foe, in fact, one of just about anything will dispatch it. The Goomba attack plan is simple: Walk forward, and hope you hit someone. Goombas are completely unaware of cliffs and will normally walk to their doom.
- Paragoombas are an offshoot from normal Goombas and are only found in one course. These special Goombas have wings, although they don't work very well, and will hop everywhere instead of walking. They are also more durable than the average Goomba, with the first bounce removing their wings and the second bounce actually killing them.
- Koopa: The most common enemy in the game, these shelled warriors can be found just about everywhere. When stomped on they will retreat into their shell, in which they will be immune to any further stomping. When the Koopas are in their shells, Mario is free to kick and chuck them around as much as he wants. Also, you can use Koopa shells to collect hard-to-reach coins, kill enemies, and hit blocks. There are 3 colors of Koopa, which are:
- Green: These Koopas are the standard lot, with and attack pattern identical to a Goomba: Walk forward no matter what the cost.
- Red: These Koopas are almost as common as the green ones. They behave identically to the Green Koopas with one difference; they don't walk off cliffs, they turn around, just like the Red Koopas in the original Super Mario Bros. game.
- Blue: This special Koopa is only found in the ice stage in Mario vs. Luigi, and it behaves exactly like a Red Koopa. When stomped, however, this Koopa drops a Blue Shell power-up to help the players navigate the vast ice levels.
- Paratroopas are an offshoot from normal Koopas and are almost as common. They will typically fly in a fixed pattern and turn into normal Koopas when stomped. Red Paratroopers always fly in a fixed pattern but some Green Paratroopas instead choose to hop around on the ground like mad, hoping to hit Mario.
- Piranha Plant: Most of these live in pipes and will come in and go out at regular intervals, exactly as they did in older Mario games. They have sharp teeth; do not jump on them, but Fire Mario can kill them with fireballs. If you are aside or on the pipe, the Piranha Plant will not come out, and you can even enter safely if it is a Warp Pipe.
- Venus Fire Trap: Some of these will spit fireballs at you; the fireball will move slowly in a straight line (and can travel through obstacles) so just dodge it. This type of Piranha Plant is rarer than in Super Mario Bros. 3, and also easier because in New Super Mario Bros. it only spits one fireball in a line, not two or three.
- A few of these plants live outside of pipes; there are even a few giant ones! They will not move anywhere unless they are on moving platforms. The giant one makes a pile of coins if Fire Mario fireballs it three times.
- Boos: They mostly appear in ghost houses, and exactly like their counterparts in Super Mario Bros. 3 and Super Mario World, they will stay still if you face them (left or right) but chase you if you face the other way. Do not jump on or touch them. Fireballs will not harm them, and they can pass through walls and other objects. The only way to kill them is by picking up a Starman and jumping at them, or by using Shell Mario's shell attack.
- Hammer Brothers: See the Moving elements section.
- Money Bags: These return from Super Mario 64 and only appear in a few courses. A Money Bag initially appears as a coin. As you approach it, it will become a bag and hop away from you. Chase it, then repeatedly jump on or fireball it to shake some coins loose, then kill it, at which point it will drop a 1-Up Mushroom.
Both Goombas and Koopas change their walking pattern based on the change in the beat of the music, at every beat a Goomba will jump slightly in the air, while a Koopa will turn around for a brief second. (Some power-ups will also bounce.)
- Moving Walls: Just as the name implies, some walls move. Be careful, as being squished can instantly kill ANYTHING.
- Yes, it can kill ANYTHING. Even if Mario grabbed a Starman or is flashing after hitting an enemy, a moving wall can kill him instantly.
- Moving walls can even destroy power-ups such as mushrooms and fire flowers. This can annoy if you are in a tower, you touch your reserve item, but it lands on a higher platform and then a moving wall destroys it.
- Spikes: Spikes will damage you on contact, stay away from them.
- Lava and Toxic Sludge: Touching either one of these will kill you instantly. Keep off!
- Spike Pillars: These are really nasty because they plow through the levels at full speed and can actually make it a disaster in some castles for you.
The easiest way to fight most bosses is for Fire Mario to shoot fireballs at them. You could also have a Mega Mushroom in reserve and let Mega Mario charge the boss. Otherwise, you may need to wait for opportunities to jump on the boss. Do not jump on Bowser Jr. while he is hiding under his spikes!
- Bowser Jr.: The boss of all towers. He must be defeated with three stomps (a Ground Pound counts as two stomps) or eight fireballs. He has two basic strategies. Which one he uses depends on whether or not he puts on his mask.
- If the mask is off, he basically tries to charge you. You can stomp him easily in this state, but watch out for his spiked shell as he comes around.
- If the mask is on, he'll adopt a tougher strategy, ducking into his spiked shell if you get close, then getting up again and tossing a Koopa shell at you. You need to stomp the shell and send it back to Junior to get him on his back. Then you can stomp or Ground Pound him as before.
- Bowser: The boss of the World 1-Castle, World 8-Castle, and World 8-Bowser's Castle; Bowser returns from the original Super Mario Bros.. Easy; simply step on the floating platform, then either fireball him to death or jump over him and hit the Skull Switch that dumps him into the lava. However, it won't be the last you see of him.
- Mummipokey: The boss of World 2-Castle. He'll pop up from the ground then start attacking by shooting at you. He'll go under the ground after you avoid his attacks. When he pops up, he'll pop up at various heights. It's best to attack him with a Fire flower or ground-pound on him when you can. You must beat Mummipokey as Mini Mario in order to unlock World 4.
- Cheepskipper: The boss of World 3-Castle. He jumps out of the water to attack, along with several Cheep-Cheeps. Stomp on his head three times when he comes up, and you'll beat him. The Cheep-Cheeps take only one hit to defeat each.
- Mega Goomba: The castle boss of World 4. This super-sized Goomba can only attack by running. By pressing the "?" Switch here, a large spring appears and you can jump on it get the height you need to get over Mega Goomba's head. You can also Wall Jump. He takes three Ground Pounds on his giant head to defeat.
- Petey Piranha: The boss of the castle of World 5. Run away from him so that he does not land on you. When he crashes into the ground, jump on him. If he is bouncing up and down, then run under him. You must defeat Petey as Mini Mario in order to unlock World 7.
- Monty Tank: The boss of World 6-Castle. He doesn't sound tough, but put him in a tank that shoots Bullet Bills and give him an infinite supply of Bob-ombs, then he does. The tank starts with only one turret layer. Occasionally he'll pop out the top and toss Bob-ombs at you. Stomp him once, though, and he'll duck back into the tank and start going on a rampage, spinning and shooting wildly. After the rampage, a second turret layer appears, meaning you have to jump higher to get up to stomp Monty. After a second stomp and rampage, a third turret appears. Now you'll need a boost to get high enough for the final stomp, either by jumping on one of the lower turrets or boost jumping off a Bullet Bill. You have to be quick, or he'll just pop back into his tank and go into another rampage. You'll also have to deal with the Bob-ombs, but if you're good enough you can throw a Bob-omb back at Monty, stunning him so you can get in a stomp.
- Lakithunder: The boss of 7-Castle. Avoid being directly underneath him - he uses lightning. He also throws spinies. When he swoops down, jump on him. Like most bosses, three hits kills him. However, the Mega Mushroom won't defeat him unless you can stomp on his head.
- Dry Bowser: The boss of 8-Castle. He is simply a Dry-Bones version of Bowser that throws bones and shoots fireballs at you. He is defeated by simply pressing the Skull Switch on the other side of the bridge.
- Super Bowser: The Koopa King returns for the final fight in Bowser's Castle. However, he's three times bigger and badder than before. Bowser Jr. is also around to face you this time. To defeat them, go after Bowser Jr. first and sends his shells back at him, then stomp him three times. At the same time, Bowser will be shooting fireballs that hone in on you. Avoid those and defeat Bowser Jr. Now, Bowser's anger will make him use stronger attacks and shoot of several blue and red fire balls. However, he will also jump. Wait for him to do so and run over and hit the Skull Switch as fast as you can. Then, you'll be rewarded with a kiss from Peach, and a special blue Toad House in World 1. If you are confident with your jumping skill, you may try to use Bowser Jr. to make a higher jump over Super Bowser, land on the Skull Switch, and enjoy the scene of both Bowsers falling down.