Accomplishing all the achievements in Word Realms requires, at minimum:
- beating the game twice, and
- beating all nightmares again on the hardest difficulty via the non-character Play a minigame option from the main menu
One of the two runs through the game can be, if you only stick to the main plot, as minimalistic as defeating 60% of the available zone opponents, and nobody from The Ring or Fight Club. You can also avoid Nightmare Village completely, or avoid Screamy's Nightmare, Rafael's Nightmare, Weald's Nightmare, and The Technician's Nightmare, but defeating Lord Nightmare the first time without playing these dreams is impossible without cheating. In other case, you technically needn't go into The Pub, defeat Wretchel, the Dreamwraith, nor return the Etherflux.
More details about individual achievements can be found on these pages: