He is always in 3v3 in the boxes if I recall, but he also drops in Survival Trial.

Dont recruit him from fragments tho,make 100 frags,and then try your luck in Time limited treasure,for 200 seal scrolls you can get him 4 stars that way

He has been available for coupons 19 Times in the last 55 weekly events. So, just under every 3 weeks since he was released. But looking at the history, it was more like one a month when he was first released and now every other week.