So looking at the description of a Sphere of Annihilation, it says:
If the sphere comes into contact with a planar portal, such as that created by the gate spell, or an extradimensional space, such as that within a portable hole, the DM determines randomly what happens […]
(Emphasis mine).
Now I have seen debates about what a Bag of Holding actually is, but I'd like to know if there's a RAW answer about what happens if you put a SOA in the Bag of Holding, specifically will it potentially destroy it? More specifically:
Is the Bag of Holding considered an extradimensional space for the purposes of the random effects of the sphere?
Best Answer
Yes, a Bag of Holding could potentially destroy the Sphere
If we look at page 225 of the 5e SRD, under the magic item Handy Haversack, we see the following:
(emphasis mine)
From this, we can determine that the inside of the Bag of Holding indeed contains "an extradimensional space, such as that within a portable hole." The logic being that if the space in the bag is close enough to that of a Portable Hole to destroy the Haversack, it is similar enough for the Sphere of Annihilation. So, if the sphere is placed into the Bag of Holding, a random result is determined by the DM, which can include the destruction of the sphere.