I would've been perfectly happy with a new Four Swords. My wife and I had a blast playing that on our 3DSs. But can we play Triforce Heroes without a stranger? Nope! And since my kid is only 9 months old, he can't exactly lend a hand at this point. So, no purchase! That was just such a monumentally stupid idea...
You could solo Triforce Hero with 2 dolls but it is cumbersome to do so because you might have to switch with dolls to get positioning correct. Like 4 Sword, Triforce is best with full team of people, and preferably without troll who intentionally sabotage gameplay by not following puzzle, not triggering the required spot, and not reaching the Triforce pad in the end. OK game as solo but get 2 friends for this one.
Are "dolls" computer-controlled players, like it was in Secret of Mana if you didn't have 3 human players?
No, they are stationary "dumb" dolls, you have to manipulate each one or carry them around. They don't follow, they don't conveniently step in the right place, or anything. It's why I suggested sticking with friends to play Triforce Heroes.
Which is an idiotic requirement. That's my point. Unless you happen to have two other people you can regularly play this with it's a complete waste of money. This is as stupid as Squaresoft requiring three people to have GBAs and connector cables to play the original FF Crystal Chronicles.