Hi Max! I’m the animator who created this transition. Shannon is right- this was all done using pre-rendered video layered over a static asset. The animation of the crystal shards forming up was created in After Effects and rendered out to an FLV with an alpha channel. The image (Taric in this case) is a static PNG underneath, that is revealed dynamically using a mask animated in Flash to match the animation of the shards.
Hope this helps! Happy to answer any other questions, but I don’t personally deal with realtime FX, just pre-rendered motion graphics.