We're very sorry for the inconvenience! There is currently a bug in the vox-l simulator that prevents you from seeing creatures in it. The bug is on our Development team's to-do list, but I'm not sure when they will have the time and resources to fix it completely.Would you like to be notified when it's fixed?
For now, try minecraft. You will be able to test any mods in there, including mystery mods, but as has always been the case, you won't be able to see vox-l pets or artifacts in minecraft.