This is NOT the Mushroom Kingdom, it is Subcon. Therefore, you can't stomp, but you can pick up your foes. 

Do NOT attempt to lift ANY bosses. Also, Birdo and Autobomb are too heavy to lift, but safe to land on. 

You will find that foes carry weight, so Toad is the only one who can lift them quickly. 

To defeat enemies, you can use Veggies, Keys, Shells, Mushroom or POW Blocks, Bombs, Bob-Ombs, Invincibility, or other foes. 

You can control your character's trajectory while in the air (Unlike SMB) 

On the NES 8-Bit version, the gray foes will appear green in the deserts. Also, Mushroom Blocks will tend to have different caps for different areas. 

The foes changed colors for the All-Stars version, here's the list: 

Pink=Turquoise (Except Panser) 
Gray=Green 
Gray Beezo=Red Beezo 
Red Beezo=Gold Beezo 

GOOD LUCK!!! (you'll need it) 
  

Red Shyguy - This small guy walks in a straight line, and will aimlessly cruise over a cliff.  Can turn in your direction if he lands on something solid. Useful, as he can carry you across spikes. 

Pink Shyguy - They pace back and forth. No real threat. 

Tweeter - Small, hopping birdie that wears a mask with a beak. That beak is sharp, so make sure to land squarely on the head of this fine feathered foe. 

Red Snifit - He's related to Shyguy. Watch out for the small bullets fired from his specially equipped mask. 

Gray Snifit - He jumps before spitting a bullet. Not exceptionally dangerous. 

Pink Snifit - Yikes! A Snifit that paces back and forth. Actually, he will turn and face you before shooting, then continue on - in your genreal direction! 

Red Beezo - He attacks by diving at you. Since you can throw off his levelling with a jump, he's not really dangerous. 

Gray Beezo - He flies straight towards you. If you get hit while on an Albatoss or narrow ledge, you'll fall off. You can't ride him, as he's too fast. 

Trouter - This little fishy fiend is quite a jumper. Try to land on him to cross gaps if you must, otherwise, toss something his way. 

Hoopster - A small danger found in a basketball-sized ladybug. Toss them off their vines, or toss a veggie or enemy at them. POWs don't even faze it. 

Porcupo - Well, since Spiny can't get into Subcon, there must be something you can't land on. And this slow crawling porcupine is it! 

Spark - A small glowing black orb that travels along the edges of blocks. Can't be grabbed, but you can shake it with a POW or other attack. 

Ninji 1 - This Ninji can run around and chase you. It jumps at times, so beware! 

Ninji 2 - This Ninji stays in one space and jumps. Not any more of a threat than a Gray Snifit. 

Subcon - Not really an enemy, these Beezo-like creatures show up at the end of the game, after Wart is beaten. Then they toss him out of Subcon and celebrate, while you get to see who did the most work. 

Pokey - A tall green cactus that crawls along slowly. You can grab it by the top and wear it down. It can't sink in quicksand. 

Cobrat - A red snake that usually lives in jars. Can spit bullets. Why it can, I don't know. Some Cobrats are also known to pop out of the sand

Albatoss - A fine feathered fiend that you can ride on. Watch out, as they carry Bob-Ombs! 

Bob-Omb - An explosive fellow, he'll do so after walking around for a bit. Blow something up with it! 

Pidgit - A small flightless bird with a magic carpet. Toss him off, and go for an air ride. 

Panser (Red) - This flower blows fireballs in an arc - and in your direction! 

Panser (Gray) - This Panser can only blow fireballs straight up, so you can actually get close to it. Jumping over it may be a problem. 

Panser (Pink) - Fireballs in an arc, and it walks too!  Very dangerous. You can't pick it up Pansers, so throw something at them instead. 

Flurry - Basically, an ice-skating snowball. It moves fast, and can follow you, but loses momentum if it turns around. Watch out! 

Ostro - This riding ostrich is no feathered friend. Toss Shyguy off, then toss Ostro at something. 

Birdo - This boss makes you so mad, you could spit! And since he appears at the end of most levels doing just that, you'd better start throwing. 

Phanto - A strange, unbeatable mask that chases anyone who dares disturb his Key. Drop the Key to get him to leave, then pick it up a little later and continue - it will take Phanto a little while to return. He can follow you through doors, but not if they were locked before. 

Autobomb - Shyguy loves to ride this cannon on wheels, and while he's on board, it will shoot fire at you. 

Mouser - This rotten rat throws Bombs at you. Return them for a dynamite finish! Boss of Worlds 1 and 3 

Fryguy -Goodness Gracious Great Balls o' Fire! And he's the hothead that's responsible. Bash him with Mushroom Blocks to chill him out premanently. Boss of World 4, which is an Ice World, of all places. 

Clawgrip - A crabby fellow that loves hard rock. Make that hard rocks! Pick up a rolling stone and rock his world! Boss of World 5. 

Tryclyde - A large order of Cobrat, hot n' spicy, with two heads on the side. You should grab some Mushroom Blocks to dispel any indigestion encountered. Boss of Worlds 2 and 6. 

Hawkmouth - When Mask Gates Attack, Mushroom Blocks are a hero's best friend. 

Wart - The baddest boss in the game, he belches bubbles (No manners), hates Veggies, and has a Veggie Maker in his chamber (No intelligence). With patience, luck, and a sense of timing, you can easily beat him.