Hahahaha.. you're funny..
Reminds me to my old day when I joined the game.
Your monster will never disappeared anytime you lose, you can still play it.
Read the how to play and understand the rulesets, you'll get better through time.
About the cards.
All cards you have in your starter packs are called ghost cards.
You can play but you can't sell or transfer it out.
You need more cards to enjoy more interesting battles and you can get it for free through completed the daily quest and join the giveaway because there's so many generous people out there.
All you have to give attention is your ECR or energy captured rate which you can view by clicking on the box before your I'd on the battle page.
You can earn the Dec through the battle too . If you win.
You can purchase the cards and the packs from the market too.