seen from United States
seen from United States
seen from United States
seen from United States

seen from United States
seen from United States
seen from China
seen from United States
seen from United States

seen from United States

seen from United States
seen from United States

seen from United Kingdom
seen from South Korea
seen from Russia
seen from United States
seen from United States
seen from United States
seen from United States
seen from United States
Based on this
The idea is that, not long after his training with Shiva, Tim went to train his skills and mind with ninja practices. Because while martial arts skills are important in vigilante work, his main skill is his mind.
The main focus was both maneuverability and creativity. The former is important, honing both agility and stealth. And while Tim did have some basic training for this, it doesn’t hurt to improve them. (Also, while his smaller stature is a point of annoyance normally, it makes him the perfect ninja. They are typically short, thin, and light, all perfect for stealth.)
Creativity is definitely his strong suit. Training to craft weapons, use them in new and unique ways, and work without them. Adding onto his existing affinity for gadgets, it just added to his existing flexibility.
His training with the bo staff was already a great start, not only giving him more physical resilience (bo staff training leads to bruising/building upper arm and leg muscles, you hit yourself a lot), but also a signature weapon that’s not difficult to recreate in a pinch.
Final point, the YJ 2019 costume already has some ninja elements to it, but I see Tim designing a suit that takes his training into account, making him the definitive ninja Robin. Tabi boots, shuko/ashuko built into his hands and feet, hidden pouches for weapons, even a breakaway cape for emergencies. The possibilities are fascinating. 
oKAY SO BATMAN NINJA GAVE ME MAJOR FEELS
But not gonna spoil it for you, JUST GO SEE ITT!!! ITS AWESOME!!!
AND LOOK AT THIS CUTIE!!!!!! MY GOD MY HEART CAN’T HANDLE THE CUTENESS!!!!!!!!!!!!!!!
Robin Annual #3