'Pattern' may be overstating it slightly but here goes..
Alexander's Underpants Alien
Requires: cheapy garish acrylic dk yarn, the brighter the better! And 3.75 mm needles. I used two dpns 'cos they were more transportable being shorter but I did have to remember not to let the stitches slide off the other end.
Cast on 30 stitches and knit 4 rows in stocking-stitch.
Next row: k1, kfb*, k 'til 2 st remaining, kfb, k1.
Next row: purl
Repeat last two rows once.
Continue in st.st for 12 rows.
Next row: k1, k2tog, k 'til 3 st remaining, k2tog, k1.
Repeat last two rows until 26 st remaining on needle.
Next: k1, k2tog, k2tog, k 'til 5 st remaining, k2tog, k2tog, k1.
Repeat last two rows once - should now be 18 st on needle.
St-st 10 rows.
Next row: k1, k2tog, knit 'til 3 st remaining, k2tog, k1.
Repeat last 2 rows once.
Now 14 stitches remaining on the needles.
Next row: cast off 2, knit to end.
Next: cast off 2, purl to end.
Next: knit first 3 stitches onto a stitch holder, then cast off until 3 stitches remaining - knit these onto another stitch holder.
* increase by knitting into front and back of stitch.
Front: as for back.
With right sides facing out, sew up one side of alien to the stitch holders - these will be the antennae/head-tentacles. Using 3 dpns (1 for each set of 3 stitches, and one spare) knit a tube up as far as looks suitably alien. This can be fiddly. Repeat for the other side, then sew up the top of the head (between the antennae). Stuffing the antennae can be tricky - in the end I put a bit of pipecleaner in the antennae. Stuff the rest of the body until comically plump, and sew shut.
Lower tentacles/arms (x2):
Cast on 12 stitches and stocking-stitch for approx. 34 rows or as long as you want really. Cut the yarn leaving a long end, thread this through the stitches from the other end pull tight. Then sew the side shut, stuff and sew end up. Repeat for other lower arm/tentacle.
Upper tentacles/arms (x2):
Cast on 12 stitches and stocking stitch for approx. 22 rows (or as long as you want as long as it's more than about 10 rows shorter than the lower ones). In the next knit row increase into every stitch (by knitting into front and back of each stitch), hence doubling the number of stitches. Stocking-stitch the next three rows, then cast off. Sew up and stuff.
Cast on 14 st and stocking stitch 39-ish rows. On the next knit row, increase into every stitch by knitting through the front and back of each stitch (as with the upper tentacles). Stocking-stitch the next three rows, then cast off. Fold in half and sew up, the foot and side. Stuff from the top and sew up. Attach each leg a few stitches in from the edge of the body.
Making up - attached the lower (longer) tentacles, and then the upper ones. Cut out an oval of white felt and a smaller oval of black felt. With black thread sew the black oval onto the white one. Then with white thread sew the eye onto the head. With contrasting yarn embroider a mouth. If it's wonky it adds to the charm, or so I tell myself.
Pants - I can't find my notes for this so it's incomplete and possibly bewildering.
Cast on 32 stitches.
2x2 rib for 4 rows.
St.st. for 6 rows.
Next two rows - cast off 3 stitches at start of each row.
Then, um, decrease at beginning of next few rows until it looks if there's enough space for the legs. St.st. for at least 6 rows - the length of gusset depends on how well stuffed his bum is - you want his pants to be reasonably roomy. An alien with Builder's Bum doesn't bear thinking about...
Then complete the pants so they're symmetrical - i.e. increase to match shape, then cast on 3 stitches at beginnings of two rows, then st.st. 6 rows and 2x2 rib for 4 rows, and cast off. I will write this up properly when I find my notes!
Sew sides of pants up and dress alien :-D. I'd originally planned to embroider them so they'd look like Y-fronts but ran out of time, so that's an option too.