Ascendant Gods

While most Gods emerge from a divine egg or red promise, it is possible for a non-divine creature to ascend to the state of divinity. To do so requires a vast source of divine energy, and even then the process rarely works for a creature not already close to a god in power.
The simplest and most reliable way to ascend to godhood is to be voluntarily bequeathed the divine inheritance of a red promise. If the promise wants to give the power and the ascendant wants to receive it, this always works. An unwilling recipient, however, introduces disharmony, and there is a risk of destructive rejection, which would kill both parties and anyone around them for anything up to a dozen miles. It would also be possible to strip the power from a red promise close to their own apotheosis, but this would both involve a struggle with the rightful holder of the power and the blood sacrifice of a young mortal, raising both practical and moral obstacles.
Even rarer, a god can choose to bequeath their divinity to another being. It is unknown if or how often this has happened, as such a transfer would also impart the donating god's aspects on the recipient, effectively transforming them into a new version of the same god.
The most common - inasmuch as any means of divine apotheosis is 'common' - catalyst is a divine egg. Any being can consume the power in an unhatched egg, granting them divinity, but there is always a risk of being consumed by the power before, or even worse, after becoming immortal, resulting in a state of unending agony.
The most significant ascendant deities are the Elemental Princes, four powerful elementals who tried to take the place of the departed Old Gods and restore the harmony of the World in the aftermath of the Colossus War. They hunted down eggs and promises alike, and once they had divine status, sought for lesser deities to consume, even as their approach to their goals became more and more absolute and unyielding.
Like the Dark Lords, the Princes ultimately faced a rebellion of their own followers. Without god-killing blades, but also unshackled by the bond of creator and created, the genies, elementals and Genasi settled for trapping the Princes in the depths of the Elemental Planes, from which they plot ever to escape, restore their worship and power, and bring their warped, apocalyptic vision of harmony to the world.