Custom potions
Beyond shop potions you can craft stronger tiers. Materials drop from monsters and come from Bounty Hunt; the Alchemist sells bottles and recipe scrolls.
What it is
The server adds custom HP and MP potions in several tiers. Lower tiers (e.g. lesser and normal) are from the shop. Higher tiers are crafted via Common Craft in batches of 50. They use materials that drop from monsters in certain level ranges and from Bounty Hunt turn-ins. One reuse group is shared by over-time (HoT) potions; another is shared by instant potions, so you can use a HoT and still pop an instant in a pinch.
Alchemist NPC
The Alchemist appears in major cities (same pattern as Buffer and Shop). They sell Empty Alchemy Bottles for adena and recipe scrolls in exchange for materials: Magic Dust, Concentrated Magic Dust, Pure Alchemy Essence, and Philosopher's Stone Fragments. Using a recipe scroll teaches you the corresponding Common Craft recipe so you can craft that potion tier (e.g. Greater, Quick, Divine Elixir) in batches of 50.
Getting materials
Materials drop from monsters in level-appropriate zones; higher-tier materials come from higher-level areas and from Bounty Hunt. Long bounties at high level can also give Philosopher's Stone Fragments, which are needed for the top-tier (Divine Elixir) recipe scrolls. Farm mobs or do bounties — or both — to gather what you need.
Crafting
Once you have learned a recipe from a scroll, open the Common Craft window and select the potion. Each craft produces 50 potions and consumes the required bottles and materials plus MP. The exact materials depend on the tier; the Alchemist's multisell and recipe descriptions in-game show the requirements.