Gears of War 4

This achievement is unlocked by upgrading 5 of your horde class skill cards to level 5.

Skill cards are unlocked by purchasing horde booster packs with credits or money, and can also be found in operations packs and elite packs. Credits are earned by completing games of versus or horde.

Each class has its own unique skill cards which can be common (green), rare (blue), or epic (purple). There are also 5 skill cards which can be applied to any class.
To view / craft / upgrade skill cards: Main Menu > Horde > Class Skills.

The cards are levelled as follows:

- 0 - Card is not yet unlocked. *NOTE* You cannot craft a skill card you don't own at least one of, you'll have to get lucky and find it in a pack first
- 1 - After receiving the first of any skill card.
- 2 - You need 1 additional duplicate to upgrade from level 1 to level 2.
- 3 - You need 3 additional duplicates to upgrade from level 2 to level 3.
- 4 - You need 5 additional duplicates to upgrade from level 3 to level 4.
- 5 - You need 10 additional duplicates to upgrade from level 4 to level 5.

In total you will need to find or craft 20 of the same card to go from not owning it to fully upgraded.

Skill cards you own at least one copy of can be crafted for scrap. Green cards will cost 40 scrap each, blue will cost 100 each and purple will cost 600 each. Scrap can only be obtained by dismantling currently owned items (skill cards, bounties, character skins, weapon skins or emblems). Dismantling a green item gives you 5 scrap, blues give you 20 scrap, purples give you 150 scrap and golds (legendary) give you 600 scrap.
As you can clearly see from this, dismantling cards will give you between 1/4 and 1/8 of the scrap you need to create another item of that level, therefore it's best to only dismantle things you're sure you don't want as it will take you a long time (or a lucky drop) to replace it.

With these figures here's the scrap it will take you to craft 19 duplicates to fully upgrade your skill cards if you choose not to rely on horde boosters:

Green: 760
Blue: 1900
Purple: 11,400

If all you want is this achievement, I would advise spending your credits / money on horde and operations packs, breaking down everything you don't need and using the scrap to craft the cards you have the most of. If you plan to complete this game you would probably be best served focusing on the cards that are most beneficial to your class instead of just the ones you have closest to level 5.

For anybody interested, a complete list of currently available skill cards is in the following spoiler tag; (I've added the maximum bonus for the cards I have fully upgraded right now, I'll update as I get more) EDIT: As of the recent horde update, this list is no longer complete. I haven't played since the update and probably won't for a while yet, if anybody is willing to share information on new cards in the comments I'll add them into the list.