[@Holy Soldier]

Boundaries can easily be set on what he can invent.  For instance, his inventions could have to be purely mechanical.  He can't make a computer or any sophisticated electrical device. If there was an active sparking thing around, he could potentially attach a stick to it and make it a rudimentary shocking tool, but that would be the extent of his electrical work.  The invention would also be dependent on what materials he does have on hand which then he would need to figure out how to solve the problem with it instead of the invention always being perfect for the situation.  Also, he would still need time to be able to process what he has on hand, figure out what he can make, then make it.

I could also start him out with a different initial ability such as the Barrel roll, where he wraps himself around a nearby person and rolls them to safety away from immediate danger, or an intuition ability that allows him to detect that something is off or about to happen(referred to as "Layton's famous intuition"). I could make the ability to fight with improvisational weapons his starting ability if you wanted. I tried the inventing one first since it is something Layton is known for and was something to potentially help him survive against veteran fighters. The inventing could become a later, higher tier ability if you wanted.

I'm sure I can figure out new abilities for Layton as this progresses.  It will be challenging at times, but Layton is one of my favorite video game protagonists.  It would be worth it.  Besides, one of those new abilities will be spent getting himself a sword.  Also, it would be fun to see what he can do after acquiring special abilities from the other realms.