A unique d3 (made of two "d4s").
When the larger pyramid lands on a side, the smaller pyramid will display the result (from one through three) facing straight upward.
Just don't step on it!
This is technically just a modified dipyramid, but since it appears to be made of two d4 dice, it could be considerd part of my "Merged Dice" series, the rest of which you can see here:
http://shpws.me/MPlv