Doesn't work with every trans according to Ross it's because of packets; Best transes it works with Lantern man, over runner, Jura/Kow.
Common transes it doesn't work with; Khanz, Dark Knight, Death hunter
Was released some time last year around when survival was released
The Hp acquired per hit will most likely (haven't tested) depend on the trans/skill used, the mob you're attacking and what kind of attack you use (jump attack/run attack). You should test these so that we know for sure
The Hp acquired is stack able so yes if you attack 2 mobs you will get more Hp but I don't know how much more.