I'm having a bit of a minor but significant argument with my DM. He feels that Alter Self can change you to any height or weight you wish, I pointed out the phrase
"You also can't appear as a creature of a different size than you, and your basic shape stays the same; if you're bipedal, you can't use this spell to become quadrupedal, for instance."
He points out it says "You transform your appearance. You decide what you look like, including your height, weight, facial features, sound of your voice, hair length, coloration, and distinguishing characteristics, if any. You can make yourself appear as a member of another race, though none of your statistics change." and that means if you want to alter self to be a storm giant you can.
I need some official input on this if you can. I assume size as used here means Small, Medium, Large etc. Am I wrong cause if I am, that makes Alter Self one of the most powerful 2nd level spells available to any class.
You can't change your size with Alter Self, a Medium creature is only going to be able to transform into another Medium creature. The spell also says none of your statistics change, which 1) would make it pointless (from a combat perspective) to try to transform into a more powerful creature and 2) reinforces the fact that you can't change size, because your size is part of your statistics.
Agreed with above. If you are a Medium size character you can alter yourself to something between a 4-foot Dwarf and an 8-foot Goliath, or any vaguely humanoid shape you can imagine within that range. If you are a small character then you can become a 2-foot Kobold or a 4-foot Gnome or similar. But above all this is a change in appearance with absolutely no change in physical function; even if you look like a (medium) Bugbear you do not gain their Long-Limbed racial trait.