Double Negative (under the supervision of Adrian de Wet ) handled the majority of the work while Asylum FX (supervised by Phil Brennan) contributed around 500 shots (roach and dragon sequences) and Rising Sun Pictures (supervised by Tony Clark and Dennis Jones) pitched in about 70 shots (CG flame, smoke and knives, texture projected face morph and concept work on mirror wand sequence). Meanwhile, Method (supervised by Stephanie Ceretti) also contributed to the climactic mayhem (cloud formation and destruction of ancient statue).
Not surprisingly, the Fantasia sequence was very challenging and time consuming for Dneg (Baruchel resorts to a short cut to get ready for a date, and, of course, the props get out of control and the lab gets flooded and Cage returns to clean up the mess).
"When we got the original script, there were only three or four lines of description," de Wet explains. "We had to make a three or four-minute sequence to build around this idea, and, given that was all we had, we went straight into storyboarding at Double Negative. We knocked out some storyboards and pretty quickly got into animation previs. After we got the turnover brief from Jon, the CG requirements seemed enormous. But it wasn't the most difficult part of the film because we knew what it was supposed to look like. Fantasia was the most daunting originally because it had to stand up to the original.
However, the final version of the sequence ended up using a lot more GG (60 shots and several hundred elements, including water splashes and environment), led by James Lewis of the animation team. "Jon is all about gags," de Wet adds, "he's all about personality, comedy, character and those little moments. Rather than the mops defying gravity, he wanted them to develop personality and interact with each other. To get that point across was the challenge."
The other big challenge was CG water interaction. Dneg used Squirt  with a whole menu of other tools, including Maya particles and DnB, the proprietary volumetric renderer.
"When Balthazar [Cage] comes in and clears all the water, you see the water vortex get swept away from the balcony, followed by a closer shot," de Wet continues. "In those two shots, everything is CG, including the water, props and floor. It was the hardest part of the sequence. It's quite difficult to direct because you can't compress fluids: they have to go somewhere, so they can't magically disappear, which is exactly what Balthazar is doing when he comes into the room. It's strange that we can't really break the rules of physics with these simulations. The software is too good in obeying the laws of physics, whereas what you're trying to do is a bit more magical than that."
"One of the most important things to Jon was that she had to look like something that we haven't seen before," de Wet suggests. "We decided to use a particle simulation to take a human form. She was a swarm of particles that gave her the ability to shape shift; she was like a school of fish. It took a long time to get there. We conceptualized this CG creature all the way along the creative pipeline. But it was late when we decided what she was going to look like: a journey into the unknown.
"We wanted her to look like a swarm and have an internal flickering energy like backlighting clouds and she had to have a density. One of our guys came up with having a thick core of lamprey eels. We needed to get a good read on her face because when we put the photography of Alice's face through the process of the particle simulation, you lost the performance. We had to dial back the solid outline of Alice and bring back some of her features, especially when she was delivering dialogue.
"What we insisted on was basing the action of the character off the performance so we didn't have to do much character animation. We did an accurate, closed body track, which involved a cloth rig on Alice, and a decent body track on her as well. We used that geometry, in conjunction with a full digital double of Alice, to generate the particles and the lampreys and all the other layers in making spectral Morgana. We altered her size because the actress isn't tall enough, so we scaled her up."
The end battle also includes the bronze Wall Street Bull coming to life (also animated in Maya) in downtown Manhattan. The challenge was coming up with a creature that both acts like a bull and a statue. "The first time, it looked too muscular and lost it metal quality," de Wet notes. "It looked too much like a bull. And so we took all the muscle jiggle out and made it tight and rigid so that it behaved like metal. And then it looked too much like a robot. So we compromised between the rigid metal Bull and the fleshy, muscular bull."
The other noteworthy challenge involved recreated the famed Tesla Coil, which is part of the apprentice's magical specialty in controlling electricity. The difficulty was in timing to the music spectacle he creates.
"We studied footage of the real Tesla Coil spewing out lightning bolts and spent weeks analyzing it and reproducing the behavior of these bolts as accurately as possible," de Wet recalls. "Initially that was done in Houdini  using L-systems. And then we had to make the bolts dance along to the music, which completely broke all the work that did. We had to turn up the contrast in the frames where they were off and the frames where the beat was. You had to really drive that home to make it look correct and in time to the music because it didn't look that way when we started."
Bill Desowitz is senior editor of AWN & VFXWorld.