This horn is enchanted with an ever-flowing spell. The ale never runs out. But, you can only drink the ale straight from the horn. If you pour it or spill it disappears in a matter of seconds. Although ale is endless, you can use its arcane effect only once per recharge.
But hey, some would argue that a plain ale is magical by definition.

Using Time: bonus action
Range: self
Recharge: sing to it old giant songs during a short rest
Duration: 1 minute

You sip from the horn (BA) or pour it into a creature (action). The drinker gains the following attributes for one minute (roll a d6):

1-2 Resistance to bludgeoning, piercing, and slashing damage.
3-4 Effects of the Enlarge/Reduce spell.
5-6 The drinker gains 10 temporary hit points at the start of each of its turns.

Upon ingesting ale, the drinker must succeed on DC 13 Constitution saving throw or suffer the following at the beginning of its next turn (roll a d6):

1-2 Suffers the effect of the Sleep spell for 1 minute.
3-4 Blurred vision gives the drinker disadvantage on all attacks for 1 minute. Casting a spell that requires a verbal component requires a DC 13 Constitution saving throw. On a fail, the spell is wasted as the caster messes up the pronunciation. Repeat the saving throw at the end of the drinker’s turn, ending the effect on a success.
5-6 The drinker starts uncontrollably and stubbornly dancing and is restrained for 1 minute. Repeat the saving throw at the end of the drinker’s turn, ending the effect on a success.

Notes: Buff, Combat