People on this site seem to mistake this game for a hearthstone-esque cardgame. It is more of a management game than anything, you basically try to manage your resources as efficiently as possible rather than playing the actual cards. Think of football manager, not hearthstone.
If you press B, you can blow yourself up.And if you manage it to kill an enemy with the explosion, you get points for the "Kill X enemies with explosives" Side Missions.
You cant kill the BLack Goblin, just upgrade your Mana Pool and the Shield Spell, Shield all your units and attack the enemies Castle with Ranged Units.Thats how you beat the Goblin Level.
 "Star Era"){kind=icon}
 "Epic Battle Fantasy 4"){kind=icon}
 "Zombotron"){kind=icon}
 "This Is Why You're Fat: In Sixty Seconds"){kind=icon}
 "Epic War 4"){kind=icon}
 "DuckLife"){kind=icon}
 "Zombie Outbreak Simulator"){kind=icon}
 "I Remain"){kind=icon}
 "A Knight's Story 2"){kind=icon}
 "Draw-Play 3"){kind=icon}
 "Fly Hard"){kind=icon}
 "Super Crazy Baseball Maniac Deluxe"){kind=icon}
 "13 Days In Hell"){kind=icon}
 "Towering Forever"){kind=icon}
 "Ametuer Surgeon"){kind=icon}
 "Trap Master"){kind=icon}
 "No Comment!"){kind=icon}