Is it safe to blend in a mango pit for the fruit juice? Is it healthy or not? Some seeds can be mildly toxic, therefore I'm asking about the edibility of mango seeds.
Yes! You're completely safe to blend in the pit in terms of healthiness. However, I make no guarantee your blender won't go kaboom. More information regarding the seeds.
Do note that other components of the mango plant can be toxic:
Mango stems, skin, and leaves can cause irritation in people who are sensitive to urushiol, the oil that causes a rash in poison oak and ivy. (source)
Consuming urushiol, if you are sensitive, can lead to a fatal reaction in your throat or stomach. If either part gets irritated and swells, you could not be able to breathe or eat anything. (wikipedia)