WotC has released a free 5e Monstrous Compendium with some monsters for the upcoming Spelljammer setting. And the Nightmare beast has been included as one of them.
I’m not sure if it can be shared here, so go and take a look if you play 5e 
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It’s something. I mean it doesn’t have psionics or many of the spells of the dark sun version but neither did the 3e version.
The one thing I don’t like is how they changed its nightmare attack to fear gas. I mean, you could make it some lair abilities to compensate for that one but still.
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