First of all, take the cards on page 3 and 4 and cut them out. You can leave out the horns and hair on page 4 if you want, or add something else in if there's another body part you want to add or an accessory that would make the monsters better. I print pages 1 and 2 on both sides of one sheet of paper.
In class, I tell the students that we're going to make monsters and then pass out the worksheet. Be sure that they write their name on the paper, because it's very important!
Next, I ask the students to draw a body, and only a body. I draw a couple examples up on the board - they can be potato-shaped, mushroom-shaped, square, or whatever else works. Once that's finished, the students should pass their papers to another student. You can have them pass along the rows or columns in the class or any other way that works for your class. The intent is that the papers should pass through many hands over the course of the activity, so the monsters come out looking silly.
When the students have passed their papers once, ask for a volunteer to choose one of the body part cards. I usually place them face-down like a hand of playing cards so the students can't see which part they're picking. Once they've chosen one, tell the class (for example), "Please draw arms!"
The students should draw arms, and only arms, on the monster in front of them. Since it's a monster, any number of arms is okay. Give them 30 seconds to a minute to draw, and then do a countdown and have the students pass the paper to the next person in the rotation. Have another student pick a card for the next body part and keep repeating until there are no more cards. I usually draw an example monster on the board and draw in each body part as the students choose cards. My experience is that the students get more and more excited as each monster fills out and looks increasingly ridiculous. I try to hold the "eye" card until 3 or 4 cards in, since eyes tend to set the "mood" of each monster and it's funnier to wait until they have more body parts before drawing them in.
Once the students have drawn the items on every card, return each paper to its original owner. Give the students a minute to enjoy their new work of art and then start the writing portion of the activity. I take the example monster on the blackboard and write out an example self-introduction.
Hello! My name is Bob.
I have three arms.
I have four noses.
I have one eye.
Students should then write their own monster's self introduction. It's good to emphasize that plurals don't apply when there's only one of something, but do apply when there's zero or two or more of something. There's a lot of room for variation in this activity, so feel free to alter it to suit your needs!