A pack of 5 classic Super Mario Bros. Enemies:

Green Koopa

Green Koopas originally appeared in MARIO BROS., their first name being "Shell Creepers". Their name was changed to "Koopas" in SUPER MARIO WORLD.

Red Koopa

Red Koopas first appeared in SUPER MARIO BROS.. In most games, they behave similar to Green Koopas, except they turn around at a ledge where a Green Koopa walks off.

Koopa Paratroopa

First appearing in 1995's SUPER MARIO BROS., Koopa Paratroopas act like Koopa Troopas, except they have wings. Sometimes they bounce, and sometimes they fly, depending on the game.

Dry Bones

Dry Bones' first appearance was in SUPER MARIO BROS. 3. Dry Bones acts like an undead Koopa Troopa, and, if smashed, regenerates. Fireballs cannot harm Dry Bones, but touching him with a Super Star will destroy him permenantly.

Feel free to use these models, but please give credit where credit is due!