ToME: the Tales of Maj'Eyal

Do you need to complete both dreams before killing the Mindworm? and do you need to 1 shot them too?

Currently, yes, you do need to finish both dreams before killing the mindworm. I think you have multiple chances to do this, unless something has changed since I did it. It may eventually be possible to complete the dreams at the altar, but currently that's not possible.

I killed the Mindworm and then, after a few attempts, did both dreams at the altar but nothing. No achievements.

theoretically, before losing them has no consequences, but if you lose them after killing him, you die dead.
from my own experience, finishing both before didn't work, and retrying the wife dream don't spawn the wife.
but the wife is supposed to be fixed in 1.3, haven't tried yet. instead, i file cheated this unlock, cause why not.

1.3 changed the dream altar so failing the dreams after killing the mindworm won't kill you for real. This incidentally removed the "danger" tag that the game looks for to decide whether to unlock sollipsist. Failing a dream generated from the place's vapors will lose you a chunk of health, iirc, which can be problematic depending on the mobs around when you're fighting.

And, yeah, the dreams have a whole slew of bugs associated with them, some recently squashed and others not. I think alchemists sometimes end up taking their golems into their dreams, unless that's been fixed.

I confirm that you can die in dreams at the altar after mindworm is dead whitout dying for "real". But I'm still confuse how I can get the achievement or if the wife dream is bug.
I have complete them both after mindworm dead: by that I meen reaching the portal with the mouse. Plus killing the elite as lost man also spawn a portal. Took them both and I get nothing.

It's not clear without a response from Darkgod. A little more detail in a bug report from Stunt over here. No matter what, you will not get the unlock from using the dream altar as is. Whether this will change (and make this retroactively, definitely, a bug) is subject to Darkgod picking a kinder design path. Since ToME isn't given to minigames, and the whole point of the altar is to make the unlock possible on your own terms, I'm inclined to think that this is a bug and some not-too-distant version will adjust the altar to allow the unlock, possibly with some additional risk.

If you feel like you deserve the unlock, it is possible to edit a text file to unlock the sollipsist. I don't know the exact process, but I'm sure it's googleable.

I will deserve the unlocked when I will know exactly what we have to do for it. I assume it's still not clear atm.
I don't want to "cheat" the class since I will have more chance to get it sooner or later with others character eventually.
I like the game too much to do that. I want the class legit or wait and investigate what happenning with the achievement.

You are supposed to complete both dreams before killing Mindworm, not after.

Double post!

It appears that DarkGod has adjusted this for the next version, about 4 hours ago.