As of 1.16 reloaded, it is possible to create custom NPCs for insertion into a game of Elona and into the current map via the F8 menu (thus, this cannot be done in wizard mode). This requires the user to choose an appropriately sized sprite and a TXT file of the format shown by the example of npc_template.txt in the Elona user folder.
After capturing a custom NPC, you gain a monster ball(user). When the ball is used, it seems to pick a custom NPC that you've imported/made randomly, rather than summoning the exact NPC you captured (need confirmation).
- Mini Guide to making Custom NPCs at the Elona forum
- Custom NPC at the Japanese Elona wiki (Google Translate)