Lv.4 missions are acquired from Mission Lobby Merchant in Gigante Beach (I6) for 1,000 reputation points. Reputation points are gained mainly through quests (including monster-hunting quests) and training a low-level family through Secret Guard (Ctrl-D). Unlike Lv.1-3 missions, Lv.4 missions cannot be traded directly.
When a Lv.4 mission is used inside another instance (e.g. Lv.2 Spotlight, Triple X Triple PvP Room), the mission item will drop on the ground instead of opening the mission lobby. Thus, to transfer a Lv.4 mission from one family to another, both families must enter the same instance, so that one family can use the Lv.4 mission to drop it, while the other family loots it after the item loses its name-tag.
For trading restricted items from boxes (e.g. Ancient Area Pass, Costume, Otite Perfume), see "Trading" Untradable Costumes.