This is an easy pattern, though it may have a couple of more unusual techniques. Since it is all knitted flat, there is a little sewing to do.

The DK jellyfish is about 4.5” (12 cm) wide, and the worsted is about 5.5” (14 cm) wide.

Yarn
You can change the size of the jellyfish by changing the size of the yarn and needles that you use.
The samples were knitted with 47 yds (43 m) DK weight yarn with size 5 needles; 25 yds (23 m) for bell, 22 yds (20 m) for tentacles.
74 yds (68 m) worsted weight yarn with size 7 (4.5mm) needles; 38 yds (35 m) for bell, 36 yds (33 m) for tentacles.

Gauge
Gauge is not important except that the knitting be firm enough that the stuffing does not show through.