Each Stormbound deck can hold as many Neutral cards as you'd like, but are limited to cards of 1 Faction only. For example: if you're using an Ironclad Deck and go to Edit it, you will only see Ironclad and Neutral cards.
To access your cards of another faction, you will need to tap on Select Deck () to switch to a different deck or to create a new one with a different faction. To view all the cards in Stormbound, tap on Collection.
Click here to learn more about Creating, Editing, and Managing your decks.