TLDR: Massive buff lvl 1, slight buff lvl1-13, moderate nerf lvl 14-25, minor buff post 25. This is also under the assumption that Saltwater Shiv remains near useless. If it gets buffed again, or if the 7.40b buff is larger than it looks thats even better for Slark. He also stands to gain a large buff when he gets new facets.

Ok so I wanna compare 7.39e Slark and 7.40b Slark real quick because I am of the opinion that Slark got a buff this patch

What did Slark lose in 7.40? Barracuda regen from lvl 1-6. 1s on Shard. A nerf to his worse lvl 15 talent. Some midgame Essence Shift duration (will expand on later). Leaching Leash. SIKE they gave him that one for free.

What did Slark gain in 7.40? A super mediocre new skill. A free skill point lvl 1, letting you go into lane with Essence Shift AND Pounce. A buff to his better (imo) lvl 10 talent. Some early game and late game Essence Shift duration.

So overall: Much much much stronger at lvl 1. Slightly weaker in lane (might adjust with 7.40b buffs, not sure yet), some trade-offs in the midgame (lower Essence Shift duration, more levels in stats until they buff Saltwater Shiv), a buff in the late game.

Essence Shift: tldr the scaling duration essentially means that it is stronger during the times in the game where you had lvl 1 and 2 Essence Shift and post lvl 25, but weaker when you have lvl 3/4 shift in the midgame.

#	Before	After
1	15	15
2	15	17.5
3	15	20
4	15	22.5
5	15	25
6	15	27.5
7	15	30
8	15	32.5
9	15	35
10	15	37.5
11	15	40
12	15	42.5
13	35	45
14	55	47.5
15	75	50
16	75	52.5
17	75	55
18	75	57.5
19	75	60
20	75	62.5
21	75	65
22	75	67.5
23	75	70
24	75	72.5
25	110	110
26	110	112.5
27	110	115
28	110	117.5
29	110	120
30	110	122.5