Item Creation
Crucible is an add-on for MythicMobs, and uses the same existing item system. This means that you simply add the additional configs to items that you've already made in your MythicMobs folder.
Crucible does not have its own Items folder.
Skills are added to items in a Skills: block, using the exact same syntax as mob skills.
For example, this item would draw a line of fire to the location you're looking at when you right-click:
SpecialSword:
Id: DIAMOND_SWORD
Display: '&6A Sword with a Skill'
Skills:
- effect:particleline{p=flame} @targetlocation ~onUse
Most mechanics and conditions from MythicMobs can be used on items - almost anything that makes sense will work how you'd expect. Crucible also supports most skill triggers, and also adds a bunch of new skill triggers, for activating your skills.
You can read more about the new toys Crucible adds for skills in the manual: