To add an event, you need to a) create an event tile in FF6LE or use an NPC to trigger an event and write your event at the address you specify in the entity, or b) use an existing event and add more to it. For the second option or even the 1st one you'll need to use the jump command B2 described
here.
To write events, Lockirby made a
good tutorial and a
document on the different event commands. You can also refer to the
event dump to see how thing are done in vanilla FF6. This last document is like a resource of many examples how to do different things.
To add Kefka as guest character, you need to create his entity (3D), add actor starting data (40), name (7F), graphics (37), palette (43) and add him to a party (3F or 3C). You can see how it is done with as an example Terra, Vicks and Wedge in the event dump. Refer to a hex editor to see all bytes:
Code:
A/5E34: 7F Change character $00's name to $1D (????? )
CA/5E37: 40 Assign properties $00 to character $00 (Actor in stot 0)
CA/5E3A: 3D Create object $00
CA/5E3C: 3F Assign character $00 (Actor in stot 0) to party 1
CA/5E3F: 37 Assign graphics $00 to object $00 (Actor in stot 0)
CA/5E42: 43 Assign palette $02 to character $00 (Actor in stot 0)
CA/5E45: D4 Set event bit $1E80($2E0) [$1EDC, bit 0]
CA/5E47: D4 Set event bit $1E80($2F0) [$1EDE, bit 0]
CA/5E49: 7F Change character $0E's name to $20 (WEDGE )
CA/5E4C: 40 Assign properties $20 to character $0E (Actor in stot 14)
CA/5E4F: 3D Create object $0E
CA/5E51: 3F Assign character $0E (Actor in stot 14) to party 1
CA/5E54: 37 Assign graphics $0E to object $0E (Actor in stot 14)
CA/5E57: 43 Assign palette $01 to character $0E (Actor in stot 14)
CA/5E5A: 7F Change character $0F's name to $21 (VICKS )
CA/5E5D: 40 Assign properties $21 to character $0F (Actor in stot 15)
CA/5E60: 3D Create object $0F
CA/5E62: 3F Assign character $0F (Actor in stot 15) to party 1
CA/5E65: 37 Assign graphics $0E to object $0F (Actor in stot 15)
CA/5E68: 43 Assign palette $01 to character $0F (Actor in stot 15)
CA/5E6B: 3C Set up the party as follows: $00 (Actor in stot 0), $FF (<Invalid Character>), $FF (<Invalid Character>), $FF (<Invalid Character>)
CA/5E70: 46 Make party 1 the current party