Zan can transform into any form of water, including liquid, mist, steam, or,
perhaps most usefully, any kind of functioning ice structure. Also, at one time,
he changed into a gelatinous form. By combining with already-existing water, Zan
could also increase his mass or volume in the water form chosen. In addition, he
could transform himself into weather patterns involving water, such as a
blizzard, a monsoon, or a typhoon.
Jayna can transform into any animal, whether real, mythological, indigenous to Earth or to some other planet, like Beast Boy. She did need to know the name of the animal in order to assume its form, as she would turn into whatever animal she named.
In addition, they had a pet Space Monkey called Gleek who had a useful prehensile tail and whose body could act as a conduit for the twins to activate their powers should they be out of reach. Gleek also served as a courier when the twins needed to travel: Jayna would typically transform into a large eagle, and Zan would transform
into (plain) water, "jumping" into a bucket which Gleek conveniently would be
holding. (This led to the joke by some fans that Gleek's superpower was to make
a bucket appear and disappear at will.
It took less than 2 weeks for me to break the daily writing about heroes. It's not that I ran out of heroes, it's simply that life got rather busy. I'm sure you know all about how that happens. Do you ever meet anyone who isn't crazy busy these days?
When I was a kid, I wished I was a twin--didn't everybody?
I loved watching the Wonder Twins, "WonderTwin power activate!"
I don't even remember their names. However, that's what Wikipedia is for!
Their powers were as followed: