Twitch Buff Idea
Give his passive a 0.05 AD ratio. The most he will deal at level 1 is 2.452 damage per second. It will stack up to 14.712 damage.
Or, it can be 0.02 AD ratio. It will deal 0.9808 damage per second at level 1. But, at level 3, it will deal 1.1008 and can stack up to 6.6048 damage per second. (That rounds to 7 damage per second).
This is way better than a flat 1 damage at level 1 to level 3.
By level 18, with no bonus AD, he can deal 5.002 damage per second with the 0.05 ratio or 2.0008 damage per second with the 0.02 ratio.
Now, with a bonus of +80 damage, he can deal 9.002 damage per second with the 0.05 ratio or 3.6008 with the other.
So, I'm pretty sure that 0.05 is the best for now, unless you'd rather 0.04 or 0.03.
0.03 at 18 would give 3.0012 damage per second with no bonus. 5.4012 with bonus 80.
0.04 at 18 would give 4.0016 with no bonus. 7.2016 with a bonus of 80.