So, how do you?

After taking Koine Greek, I have trouble pronouncing any Greek word that has an "o" in the last syllable with the long-o sound. So, I end up saying something like: "Their-ahs" or "Purf-or-ahs."

I've noticed most other people use the long-o sound, so "Their-ohs" or "Purf-or-ohs."

I guess it depends on whether WotC intended to use the omega or omicron...

thair ohs

Has WotC ever made a pronunciation guide? They really should.

~SE++

The Ross

MaRo does pronunciations on his Tumblr every now and then if people ask.

theer ose

You could just listen to that little advertisement thing that they make whenever they announce a block. They say it in that.

Th as in thank, er like air, os like glucose.
Th-air-ose

True, but not all names are pronounced in the videos, and especially in a set like Ravnica, there are a lot of individual groupings all covered under various unique names.

~SE++

They did make a pronunciation quiz. Though it doesn't include "Theros" itself, all the other words with -os as their final syllable are pronounced with the long o. Even if that's not standard Greek pronunciation.

I think an early intent might have been to put a soft th- sound in front of the same sound as "heroes" — so something like "thear-ohz" or "thear-ohs." But that sounds dumb to me (the latter less so); instead, I use the same pronunciation Lily used with a soft th-, "thair-ohs."

You could go back to some of the Pro Tour Theros recordings. I'm sure Rich Hagon says it like 20 times an hour.