I have up-sized my ‘Pikachu’ by using this tutorial to turn one strand of 8ply yarn into 3;
https://www.youtube.com/watch?v=gGKgRuWrk_Y&fbclid=Iw...

And I’m using a 5.0mm hook.

He came out kinda chubby….but I love him! :)

Detective Pikachu Cap
(Hat pattern will work for your Pikachu if you use the same yarn and hook size as used to make your Pikachu.)
Using 3 strands of 8ply yarn and 5.00mm hook,
work 6sc in a magic ring.
Rnd 2: inc around. (12)
Rnd 3: (1sc, inc) around. (18)
Rnd 4: (2sc, inc) around. (24)
Rnd 5: (3sc, inc) around. (30)
Rnd 6: sc around. (30)
Rnd 7: (4sc, inc) around. (36)
Rnds 8 - 10: sc around. (36)
Finish off.

Peak for cap
(Make 2)

Row 1: Ch 12, 1sc in 2nd ch from hook, sc to end, turn. (11)
Row 2: Skip first sc, work 9sc, turn. (9)
Row 3: Skip first sc, work 7sc, turn. (7)
Row 4: Skip first sc, work 5sc, finish off.

Sew one peak on to the front of the hat and one on the back.
I worked 1 round of reverse single crochet (using just 1 strand of yarn) around the bottom edge of the hat - including both peaks - this makes the peaks more rounded.

I worked surface crochet over the top of the hat - in a cross - and added a small bow to make it look like an old-school detective hat.