Buddhism has its own ontology. It's not a speculative attempt to describe ultimate being or the one true reality (e.g., the One Mind as the perfect eternal form) but, instead, an invitation to realize true reality in our very self (pratyatma). This means also that the realization of true reality is a subject beyond the efforts of philosophical speculation to represent. It is also beyond the ken of sensory consciousness. This subject, in addition, is not a phenomenon. Nor does it exist within time.
As far as being anything reachable by the senses by which they might be gratified, such an ontology is not. Realizing nirvana or the One Mind in the very self is not meant to bring happiness to our conditioned, worldly existence which inevitably ends in death. Such a world of transformation and change is never other than degrees of suffering: a kind of disharmony (duhkha) which never comes into complete harmony with itself.
Ultimate or true reality, on the other hand, does not change or transform. It is in perfect harmony with itself; but such a harmony is not apparent in our temporal world which is constantly changing and transforming. This seeming duality is reflected in the analogy of the water element (self-identity) and the waves (change) or the clay and the vessels made from it, or gold and the objects made from it. The artifacts or objects we perceive are maya which literally means 'not that'. Logically, illusion or maya must appear (a non-appearing illusion is absurd). Phenomena, therefore, are never other than illusory—they are not the absolute. In addition, there is no real duality.
Our conditioned, illusory world is like a huge veil which is empty (shunya); which has no existence of its own (svabhâva) because there is nothing ever stable within it. This veil is also avidya, that is non-knowledge. For us, to be more precise, avidya is the inability to distinguish between this dazzling, illusory veil in which we are entrapped, and ultimate reality. As an example, we can't distinguish between our various thoughts and the substance from which they are composed, so powerful is the illusion. This powerful illusion cloaks our true nature. The depth and degree of avidya is almost overwhelming. Penetrating such a veil is no easy task. A half-hearted endeavor will always fail.