I love origami art, and square and rectangle shaped sheets of paper are the most common shapes used for it. I was wondering what other possibilities there could be with a triangle shaped paper, so after trying many ways of folding it, the best result I ended up with was this one: a little piranha.

Supplies

1 square or rectangle of paper, double-sided (minimum 20cm side)
1 Cutter or scissors
1 Tool for Fold (optional)

Step 1: Cut a Triangle

If you have a square paper, step A.

If you have a rectangle paper, step B.

Step 2: Put the Color Eye and Teeth, Up

Step 3: Pinch

Step 4: Fold Until the Reference, Fold Both Sides to the Center and Unfold All

Step 5: Check the Reference and Fold

Step 6: Close the Paper Using the Existing Creases, Turn the Paper Over and Rotate

Step 7: Fold

Step 8: Open and Flatten As Diamond Until the Reference

Step 9: Fold

Step 10: Getting a Smile

You should pull out the first layer, note that the paper is moved, it is normal, you can solve this flattening, don't worry if the tail has a gap, we will solve this later. If you have a problem folding the mouth, you can unfold and turn the paper over as it is shown in the picture 4 to adjust it.

Step 11: Hide the Little Tip From Eye, Fold

Step 12: Pass the Layer to Front, Pull Out

Step 13: Fold, Pass the Layer to Front, Fold the Two Layers Until the Reference, Up the Two Layers

Step 14: Open the Layers and Fold, Fold a Little Curve for Trap the Tail

Step 15: Fold

Check the points for fold with the pictures.

Step 16: Fold

Step 17: Fold Pectoral Fin

Step 18: Fold, Fold Dorsal Fin

Step 19: Adjust the Tail

The position of the tail is wrong, so, fold a zig zag, turn over the figure and make a little fold to trap the tail.

Step 20: Details

Do you remember the paper gap? In case you have another color left visible on the tail, make sure to fold one more time in order to hide the mismatch of colors so that its shape can appear neater.