KINGDOM HEARTS HD 2.8 Final Chapter Prologue

This achievement will unlock when you have owned at least one of every command available in the game. You do not need to own them all at once but I do advise that you sell none until you have unlocked this achievement.

The reason for this is that some commands are only available in shops so when double checking those it will be painful to know what has already been counted and you will probably end up buying them all back anyway. The commands that count towards this trophy are Attack, Magic, Items, Movement, Defense, Reprisals and Flowmotion. To collect all commands make sure you do the following.

Complete the Story.
Collect all Treasure Chests
Check the Moogle Shop on a sale day (you can check this via the forecast screen by pressing in the main menu or world map) and buy any commands not owned.
Check the Flick Rush Medal Shop after reaching rank 20 (see Flick Rush Fever for details) and buy any commands not owned. *Don't forget the Item commands*

This should leave you with commands that are only available through spirit link boards and one command that can only be purchased as a random Drop Bonus after you have reached Country of the Musketeers. Here is the list and requirements. If a spirit is marked as needing a specific disposition you will have to change this in order to unlock the ability to change it, to change it you need to poke it or feed it, some have 2 secret routes others have 1 and some of them doenst have any secret routes, unhappily I didn't find a faq about it, if somebody wants to cooperate would be very helpful.

Blackout – Peepsta Who link board.
Break Time – Halbird, Me Me Bunny link boards.
Dark Aura – Ghostabocky , Keeba Tiger link boards.
Dark Break – Cera Terror, Fishboné link boards.
Dark Firaga – Kab Kannon link board.
Faith – Aura Lion, Flowbermeow link boards.
Icicle Splitter – Iceguin Ace link board.
Mega Flare – Ryu Dragon, Tyranto Rex link boards.
Meteor – Keeba Tiger link board or The World that Never Was A-Rank dive reward (see Ace Diver).
Meteor Crash – Ryu Dragon, Tatsu Blaze, Tyranto Rex link boards.
Poison Dive – Fishboné, Toximander, Woeflower link boards.
Rapid Descent – Electricorn, Tyranto Rex link board.
Sleepga – Tama Sheep, Woeflower link boards.
Sliding Block – Random Drop Bonus after reaching Country of the Musketeers. *Keep an eye out for this while completing post game*
Steep Climb – Cera Terror, Halbird link board.
Superglide – Ryu Dragon link board.
Vanish – Ghostabocky link board (Split Personality disposition required).
Zantetsuken – Cera Terror, Lord Kyroo, Staggerceps, Thunderaffe link boards.