From what I can tell, it looks like it was build up of a rectangle, the portalglow bitmap, a bunch of random instances of the portalparticle bitmap and an animation or a gif of the moving parts on te portal.
But I don't see any bitmaps for the last part, am I missing anything or is that animation generated in realtime?
How was the portal animation made?
It's generated in realtime.
The code for it is in game.lua and portalparticle.lua if you're interested.
The code for it is in game.lua and portalparticle.lua if you're interested.