Land of Carnage: Enter Post Game by defeating the Final Boss and not getting a Bad End.
Etna's Hidden Room: You must clear 10 floors in any single item, ever. That lets you change who you control in the base, and who follows you. Remove Etna from the group you walk around the base, then the same way as in the first game, examine the back of the Throne, and the Skull by Shops, then examine the corner in the library section, near the scene viewer NPC.
Longinus: Slightly changed. IIRC, you need 21 Spear Mastery on a character, then you need to make that character into your base Leader, and talk to Zommie. --- Spell card! Diamond Will ~ Unbreakable Determination!
Cheat Shop for LoC. In the Garden, turn the camera, the NPC is a Male priest.
Time Traveler is to access New Game Plus, aka NG+. You start over from Chapter 1, but you retain EVERYTHING from your previous playthrough other then Story Characters. When a story character rejoins, they we be EXACTLY how you left them. --- Spell card! Diamond Will ~ Unbreakable Determination!