In one corner -
A large goat that can walk on its own hind legs.
In the other corner -
A leprechaun of relatively large physical stature (for a leprechaun) who possess mischievous powers
Verdict: This is the kind of battle that you might have found up a mountain in the Burren 5,000 years ago, and then and as now, I think the leprechaun jukes and jives, avoid the thrusts of the goat horns and eventually triumphing with a bit of magic.