MemeMana is the essence plugin, which is new in the 1.12 update.
Mana is a virtual resource you get for playing on the server. If you log in multiple days in a row, you get a login streak, meaning you get more Mana each day. If you stop logging in, your streak will go down over time. This means that logging in each day will give you the most Mana, but if you miss a day, it's not that big of a deal.
Mana allows you to fuel Exile and/or Prison Pearls. Each unit of Mana refills a single pearl by a certain percent. The the pearl's health decays over time, so you must refill it with Mana every so often to keep it from getting to 0% and disappearing.
You also need a significant amount of Mana to upgrade an Exile pearl to a Prison pearl.
When you log in, you will get a message telling you how much Mana (if any) you got for logging in.
You can check your total amount of Mana at any time by using /manashow or /mns for short.
To refill a pearl, hold it in your hand and type /manarefill to refill it as much as possible, or /manarefill Amount to refill it using up to Amount Mana.
To upgrade an Exile pearl to a Prison pearl, hold it in your hand, then use /manaupgrade.
Type /manatransfer Someone Amount to transfer Amount Mana to the player or NameLayer group Someone.
If someone transfers Mana to a group you have the MEMEMANA_WITHDRAW permission on, use /manawithdraw Group Amount to move the Mana from the NameLayer group to your personal account.
Then you can use /manarefill (see above) to refill pearls.
If you don't use your Mana to refuel pearls, it will eventually decay, meaning it disappears completely.
This mechanic exists to solve the "coal problem," which is where vault owners have big enough stockpiles of coal that it doesn't really cost them anything to fuel pearls.
If the pearl fuel (Mana) decays over time, then they can never have more than decayTime * activePlayers * manaPerPlayerPerDay units of mana stockpiled.
This means that vault owners can only keep a certain number of players pearled indefinitely, or they will run out of Mana once their (limited) stockpile runs out.
The exact amount of players that can be kept permanently depends on how many active players give their Mana to the vault owner.
It is possible to set the ratio so that, for example, one active player's Mana is enough to keep one player permanently Prison pearled.
Your virtual Mana can be materialized into physical Mana, but beware: physical Mana can't refuel pearls, and it can't be converted back into virtual Mana.
Physical Mana is currently useless, but it might have a use in the future, like converting it to XP, or using it as an instant payment system.
That said, you can get physical Mana by typing /manamaterialize and then clicking on Mana to materialize it.
Hovering over the Mana in your /manamaterialize GUI will give you detailed information about when it will decay.
/manainspect <Player or Group>