Map mobility, power farming, and assassination.
Burst damage and target access
Champions, large minions, and large monsters drop soul essence on death. Touch souls to absorb them and deal bonus adaptive damage on your next attack based on total soul essence collected.
Gain a burst of Lethality and Magic Penetration after using a dash, leap, blink, teleport, or on leaving stealth.
Collect eyeballs for champion and ward takedowns. Gain permanent AD or AP, Adaptive for each eyeball plus bonus upon collection completion.
Unique champion takedowns grant permanent out of combat MS.
+18 Ability Power or +11 Attack Damage, Adaptive
Gain 3% extra MS. Gain extra AP or AD, based on your bonus MS, Adaptive.
Gain MS and AP or AD, Adaptive when in the river.
Nidalee's ability to farm the jungle incredibly quickly means you'll be able to build Dark Harvest stacks very efficiently for that mid-game burst damage.
Nidalee's high mobility with Pounce allows her to keep the Magic Penetration and Lethality buff up at almost all times.
In human form she can make use of that Lethality with ranged auto attacks.
As an assassin, you're wanting to pick up kills around the map from as early in the game as you can. Doubling down on that, we can take Eyeball here for even more power to snowball.
Also, as a Jungler your often clearing a lot of wards with sweeper and pinks, gaining even more stacks.
Nidlee is a Jungler who excels at clearing her jungle insanely quickly and getting around the map to find any fight she wants.
Relentless Hunter gives you the mobility, when paired with your passive, get form one side of the map the the other in the blink of an eye.
Celerity synergizes pretty well with Nidalee's passive, granting you more AP when entering a bush. The bonus Movement Speed also furthers your ability to get to fights anywhere on the map.
Waterwalking allows you to massively control the river and quickly invade the enemy jungle with your fast jungle clear time.