Something else I would like to see would be Manipulation of State of Matter. To turn something liquid, solid or gas, or even plasma. It'd also allow the user to shift between solid, gaseous, liquid and energy form too.
Powers revolving around just a slime form would be interesting as well. The slime version might have assimilating powers by extension.
Weapon conjuration or creation would be neat. Either by forming weaponry from thin air, or by pulling it out of the character's body/form it from a fragment of the character's body (like hair). Or just turn limbs into weapons, of course. It'd fit well with a 'living suit of armor' character. Might result in Ghost n' Goblins gags, what with Arthur being able to throw an entire armory's worth of weapons.
While not listed as one of their abilities, a lot of characters can make clones. Suwako can definitely make a whole bunch of them.
Remilia can also do it, and many other stage 6 characters.
I would like to see manipulation of speech. Getting people to say the wrong things will be hilarious.
I believe you mean Suika, not Suwako, unless I'm missing something here.
Yuuka, Flandre and Parsee are also capable of creating clones.
Touhou have a kunai bullets, but there's no a ninja yet? BLASPHEMY!
Hmmm..
Power to become "justin bieber"
Power to become "rebecca black"