1: Oxygen is pretty amusing. (3)

3: One with no trust in decency, niceness, etc. (5)

5: This would make me a lord (7)

7: Immediately placed in an awkward situation (2,3,4)

9: Medicine was our connection, we hear (7)

11: Game for drunkard (5)

12: You audibly ram partner (3)

1: Mug returns to 100 degrees, causing an ulcer. (7)

2: Fish in sea initially react to heat, perhaps (5)

3: Confined bear without a trade (9)

4: Agree to make Lucifer wicked? (3)

6: Bill is taken in by drug smuggler being inconstant (7)

8: Its out-of-date to need a permit for the course (5)

10: Vet theatre opening 8-down (3)