Greg responds...

Magic powers the Phoenix Gate. The idea for the gate came to me in a fevered
dream (well, actually in an editorial panic), while we were working on
"Vows". We new we needed a maguffin for that story. Something that both
Xanatos and Demona would want to get from Goliath. Something that Goliath
associated with his love for Demona, but didn't know the true nature of.
Originally there was no time travel in that episode. Then I came up for with
the idea of the Gate for the maguffin. I squashed the entire episode into
Act One, so that we could have two acts of time travel. That's one reason,
why that episode might seem a little rushed. It really should have been a
two-parter.