There is no specific gauge as it's a toy. Just make sure your stitches are consistent throughout to get the ride sizes for each piece.
When made from DK weight yarn, Poliwag is about 16cm in height and 17cm from stomach to end of tail. The features (eyes, mouth, spiral and white part of the tail) are all needlefelted and instructions are included on how I accomplished this.
This pattern will not include a tutorial on how to crochet or needlefelt. You can find tutorials for this everywhere. I learned to crochet from http://www.freshstitches.com/. I learned to needlefelt from http://woolbuddy.com/.
If you don’t want to needlefelt, you can always buy felt sheets in white, please, pink and black and cut out the features to sew or glue on instead and you can skip all of the eyes, mouth, stomach instructions.
To make the poliwag like in the picture, you will need:
Blue DK weight yarn
G/6 – 4.0mm crochet hook
Wool Roving – black, white, pink, red