I've taken to playing DOTA 2 recently, and I really enjoy playing Templar Assassin. Here's an attempt to work her into league in a balanced way. For those of you who don't know, TA's kit in DOTA is:
No passive (dota heroes don't always have a passive like in league)
Q: Bonus damage on next 6 autos, take no damage from the next six instances of damage (6 at max rank, anyway)
W: Instantly enter stealth, permanent until you move (like Teemo). If you break stealth with an autoattack, it does a ton of damage and reduces their armor by a lot.
E: Bonus aa range (She starts as a melee, ends as a low-range ranged champ), on-hit damage spills as true damage onto targets directly behind.
R: Place a trap at long range, traps can be manually detonated to slow targets nearby by 30%. Slow amount increases by 5% per second the trap remains there, to a maximum of 50%
Reasoning for what I've done: Passive: Her E in dota is now her passive, because I needed to free up one ability slot. it scales with level, so that you have a tristana like effect, albeit you end up with a still very low range. Damage changed to physical.
Q: Same thing. Added some scaling to it, because abilities in league scale. You might think "omg damage immunity so op", but I don't think so given it's high cd, high mana cost, and the fact that it gets absolutely shredded by DoT abilities. In DOTA it also gets shredded by creep aggro, but since there are more creeps in league, and more ranged creeps, I decided to remove that part.
W: Same thing. In dota she MUST break stealth with an autoattack to get the bonus damage. I've decided to give her a .75 second window to attack, because she'll be melee for a good portion of the game and doesn't have the option of increasing her range manually like she can in dota when she needs it.
E: I've moved her ult to her E and given her a new ult. You'll see why. As it's a basic ability, I've lowered it's range by a lot, so she has to rely on pre-placing traps. Because it doesn't have stupidly high range anymore, it's got a flat 50% slow.R: In dota, TA is very reliant on Blink Dagger as a positioning tool. In league, there is no Blink Dagger, and there are a lot more mobile heroes. What she has is a blink with a low(ish) cooldown and a reasonably long range. It can't be used as an escape because it goes on a 3 second cd whenever she takes damage from a champion. Basically, it is exactly the same thing as a blink dagger, because she really needs one of those to be remotely useful.