Overdraw: This will kill your framerate if you are using alot of alphaed surfaces/particles, as each alpha pixel will have to be blended with whats on the z-buffer. So, keep that low or to a small area of the screen if possible.
Animation: Using boned animation in blitz is fairly slow. The more bones you have and the more bones per vertex, the slower things will be, as it's all done by the CPU, instead of the GPU.
Mixing 2d with 3d command: This can cause a big slowdown, depending on your hardware, so avoid if you can.
The Text command: probably partly to do with the above, but this seems to be the slowest 2d command and cause major problems on some systems.
To many polygons or high res texture: This is dependant on your GPU's fill rate.
Animation: Using boned animation in blitz is fairly slow. The more bones you have and the more bones per vertex, the slower things will be, as it's all done by the CPU, instead of the GPU.
Mixing 2d with 3d command: This can cause a big slowdown, depending on your hardware, so avoid if you can.
The Text command: probably partly to do with the above, but this seems to be the slowest 2d command and cause major problems on some systems.
To many polygons or high res texture: This is dependant on your GPU's fill rate.