From the Super Mario Wiki
The Megalixir is an item found in the game Super Mario RPG: Legend of the Seven Stars. It is a superior version of the Froggie Drink and Elixir. When used, it recovers 150 Heart Points to all party members. Megalixirs can be purchased from the Juice Bar shop in Tadpole Pond after acquiring the Tenor Card. It can be bought for 90 coins with the Tenor Card and 60 coins with the Soprano Card. The selling price for the Megalixir is 60 coins.