My advice would be to just pull the last few 10x draws and get him, but in future, don't waste so many scrolls on one ninja. The ninja tend to be cheaper or the same price in events as the price of the scrolls would be were you to buy them. So save coupons and buy ninja if you want them, use scrolls on the most relevant draw, not a low tier one with no longer useful ninja in it just to get one useful ninja.

Just my advice, take from it what you will.