You know a magic item is good when they have warnings and this one has several in multiple languages. 
1. Do not drink if you are not at a legal age for alcohol consumption. 
2. Tinkles, his shop, and his associates  are not responsible for any side effects incurred through drinking. 
3. Have a good time and drink away your sorrows. 

You may drink one vial of Mystery Eggnog as an action. If you drink more than 1 vial in 1 hour make a constitution saving throw. The DC is 10+vials drank in the hour. On a failed save you become drunk. While drunk you have disadvantage on attack rolls, saving throws and ability checks, but are immune to fear. You remain drunk for 1hour+1 additional hour for each vial drank that hour prior to the failed save. 

After drinking the Eggnog roll a d20 and consult the flavor table for the associated taste and effects. The effects of the flavors do not stack and by drinking additional Eggnog your previous ability is replaced with the new one. The vial can contain up to 20 cups of brew depicted as charges. 

Flavor Table 

1. Are you Gnoming Kidding: This sweet blend is made from the sap of a Whiskeywood fir. The alcohol content of this brew is so high, even the strongest instantly get drunk. As a result you become intoxicated for 8 hours. 
2. Glass Bottom Boat: This salty blend is derived from algae. After drinking this brew you grow gills if you didn’t already have any or additional ones if you did. After drinking this brew you can breathe underwater for up to 8 hours. 
3. Apple Bottom Gnomes: This fruity blend is very pleasant to imbibe. After drinking this specific Eggnog you are filled with glee. For the next hour you have advantage on all charisma checks and saving throws.
4. Peppermint Hop Schnapps: This minty blend goes straight to your thighs. While not great for that slim summer look, it is great for leaping homes in a single bound. For the next hour your vertical jumping distance is now 20 ft from any solid surface. 
5. Ode to Starfallen: This rather earthy blend is a testament to the Great Leaders of Starfallen. Your muscles swell to the size of the founding titans. You have advantage on all strength checks and saving throws for the next hour. 
6. Beholder’s Gaze: This rather acrid concoction is not an enjoyable experience for most casual drinkers; however the side effects are simply too good to pass up. After drinking this concoction you grow a large eye at a location of your choosing. All magical effects within a 30 ft cone directly in front of the eye are nullified while inside the cone. The effect ends once  the magical item leaves the gaze. Magical attacks that pass through the cone are also nullified. The eye lasts 1 hour or until the drinker is knocked unconscious. 
7. Quickling: Who needs taste when you have pure unadulterated speed. You’ve never felt so alive. Your speed is doubled for the next hour. 
8. Miracle on 43rd Drive: This berry blend drives you mad with lust. The next humanoid that you would otherwise find attractive becomes your obsession for the next hour. Your only goal while under the effects of this concoction is to achieve true love’s kiss and move to an island with your soulmate. (Tinkle wants to reiterate here that consent is VERY IMPORTANT). 
9. Nightmare Over Starfallen: This dark blend, leaves you shivering and cold. Your sclera and pupils are replaced with a onyx gleam. While under the effects of this drink you have dark vision up to 120ft for up to 8 hours. 
10. See Ma Drinking Makes you Smarter: Legally this isn’t books mixed with eggnog. Pay no attention to the floating pieces of parchment and ink.  That’s um… clearly um… magic stuff. Tastes dewey. After drinking this brew you have advantage on intelligence checks and savings throws for 1 hour. 
11. Nobody’s Home: This blend tastes like pizza. How that works may be the greatest mystery of any of these flavors. After drinking this potion you shrink to 3ft tall and are considered small. If you are already smaller than 3ft no change to your size is noted. You remain small for 8 hours. For those 8 hours you are overcome with an insatiable bloodlust for revenge. If you are damaged by a creature you will not stop attacking that creature until it is unconscious and you can not use the help action on any of your turns. 
12. Heart Attack: This blend tastes like the greasiest potato fingers you’d ever experienced. After consuming this beverage your heart grows three sizes and thankfully utilizes magic instead of logic for function. Your oxygen carrying capacity vastly increases and you have advantage on all constitution saving throws for the next 8 hours. As an unrelated bonus all your hair turns green. 
13. Royal Swap: This blend tastes of oysters, caviar and the finest wine. For the next 8 hours you become become a distinguished member of a royal family. Practically all this does is give you expensive taste. You are incapable of bartering and when you hear a negotiation in progress you become viscerally offended if you or your allies try to talk down the price. Also, you refuse to do any labor you deem beneath yourself, including searching corpses, reading etc.
14. Ruby Schnoz: This blend tastes of venison and lilac. After drinking this blend your nose is wreathed in a warm Ruby light for 8 hours. This casts bright light for 30 ft and then dim light for an additional 30 ft. If the drinker lacks a nose one will be formed in the general location. 
15. A Journey of Resurrection: This blend tastes like red wine and crackers. Much like Sujes The Holy Paladin, if you fall in battle over the next 8 hours you are sworn to return in exactly 3 days, as though unscathed. 
16. Hear them Sleigh Bells Jingling: This blend tastes like crisp snowy air and frozen vegetables. After drinking this potion you are transformed into a gorgeous white furred reindeer for the next 8 hours. This acts similar to the polymorph spell in that you gain the stats of the creature for the duration or until you drop to 0 HP. For creature stats you can use an Elk. 
17.  Loud Night: This blend is remarkably strong, made from the Screaming Willows of the Northern Pass. After drinking this Eggnog, for the next 8 hours you are incapable of speaking below a yell, crunch on every loose stone and ensure that your movements are as loud and exaggerated as can be. You have disadvantage on all stealth checks.
18. Fruit Smoothie: This is literally just a fruit smoothie. Tinkle must have gotten so drunk and mixed this in with one of the batches. This is the most powerful of all though in that it restores all your depleted vitamins and comes equipped with multiple anti-oxidants. You do not need to save against intoxication after drinking this smoothie. You feel refreshed and rejuvenated and your skin glows, in a metaphorical sense. No light is actually radiating from you.
19. Charlemagne the Black: This rather dark blend, tastes mostly of peanuts. After drinking this potion you become incapable of understanding anyone considered an adult. Instead you hear only indecipherable babble for 8 hours. You do however understand all humanoid children and beasts regardless of language spoken. 
20. Hark the Herald, Angels Fly: This celestial blend made from ambrosia and holly garners you a brief glimpse of Elysium. After drinking this potion you grow angelic wings with a wingspan equal to your height. The wings are red, green and white and grant you a flying speed of 100 ft. You also speak Celestial as long as the wings are active. These effects last 1 hour.