What the elf is an 'add2' chord? Why nobody told me? What else are you hiding, ToneGym??😁

An add2 is a major or minor triad (root, third and fifth) but with the second added in as well (root, second, third, fifth).

I didn't want my comment to sound disrespectful towards your question, @Neil Gilmartin . I'm sorry if that was the case, but my only intention was to joke about the fact that, despite all the years of studying music theory plus 2 on ToneGym, I wasn't aware of the existence of a name for such chord extension -being some kind of alternative sounding add9.
I just need my imagination to know that the sound of such artifact is not going to sound pleasing to me, unless it's arpeggiated, so I got a little 'shocked' when I saw 'add2' written down for the first time. It was perfect material for a joke, please bear with me...

Wait! Then there must be also an 'add4'...!😂

This article might be helpful for you-
https://www.tonegym.co/help/item?id=how-can-i-learn-from-my-answers-in-the-gym-games-compare-mistaken-answer-with-the-correct-answer&f=0

It didn't sound disrespectful, Cuantas. That never even crossed my mind. But yes, in the game, the option of add2 is given, not add9. I guess they are literally adding a second note below the major 3rd rather than than an octave up. But still, my point was that I'm sure what I was hearing was a major triad - no additions, no extensions - yet the answer was 'add2'. Although I am starting to doubt myself now...

It might be a bug. Maybe you should report it?
Add2 chords don't exist. if all 4 notes are within an octave, it would be a block chord and it would still be called an add9

The discussion about the 'existence' of Add2 chords is sterile. The fact that I haven't ever consciously listened it, or seen it written down on any staff I can remember, or even my opinion about its absurdity can never imply that chord doesn't exist. 'Exist' is a big word...

From an excellent ear training course on macprovideo / ask video.

I think it's valid to use 2, 4, and 6 when you don't have a 7 in the chord. Using 9, 11, or 13 implies that there is also a 7 somewhere, but using 2, 4 or 6 makes it clear that there is only the basic triad and then the addition of notes below the 7, not an extended chord in other words.

Can’t delete that post above for some reason…

Sure, there's been lots of time I've been wrong when I really thought I was right. ;)

Your last explanation makes total sense to me. It's always nice to learn new things, and it's great to have this helpful community!! Thanks @Neil Gilmartin !