Otherwise known as the Manual of the Planes?![]()
IIRC, in the playtest document 2e's Tieflings were renamed as "Planetouched" and are a blanket category for "humans with extraplanar blood". The Tieflings in the PHB will be probably 4e ones.What's going to be interesting to see is how they define tieflings, and if it favors the classic 2e/3e version or the rather different 4e version.
They aren't my favorite (And why isn't Aasimar a base race if Tiefling is one?), but it's just fine since they didn't exclude former base races to include them.
I agree you can do a lot with them, if you imagine them more thematically and less as a brutally oppressive "AHH, I'm (burning/buried/drowning) alive!". Caverns a mile high, filled with iridescent rocks and glowing fungus for the Plane of Earth, for example. Or cloud palaces, connected by soaring golden bridges for the plane of Air.Also known as "My Favorite Book of All Time Ever". The original one, at least. I also think that the Inner Planes and demiplanes influenced by "classical" elements are underutilized. But I know that's not a popular opinion.![]()

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.