Tusky by MagicPants

Tier 1:

Hyperactivity: Metabolic Boost's duration is increased by 2 seconds.

Minion Feast: Killing an enemy minion heals you for 10% of your max health.

Hunt the Weak: You deal 1% additional basic attack damage for every 1% of your targets missing health.

Tier 2:

Pack Hunter: Your damage against enemy minions and mercs excluding bosses is increased by 100%. You also take 75% less damage from them.

Throat Slash: Leaping Attack will silence the target for 1.75 seconds. This effect has a 10 second cooldown.

Ambusher: Your first basic attack within 3 seconds after exiting a bush is increased by 100%.

Tier 3:

Zergling Rush: Activating Metabolic Boost makes you unstoppable for 1 second.

Zergling Momentum: Your basic attacks reduce the cooldown on your basic abilities by 0.5 seconds.

Follow Through: After using an Ability, your next Basic Attack within 6 seconds deals 40% additional damage.

Tier 4:

6-Pool

Wild Mutation

Tier 5:

Speedling: Enter stasis for 2 seconds and emerge a Speedling, increasing your movement speed by 50%. Future summoned lesser zerglings will also be speedlings.

Devouring One: Enter stasis for 2 seconds and emerge a Devouring One, increasing your max health by 50%. You can no longer summon allied zerglings through your trait, instead every 1 essence you have will reduce your death timer by 1 second. This essence is consumed on death.
Quest: Collect essence to empower Zergling Reconstitution. (including essence already collected)
Reward: After collecting a total of 100 essence you permanently reduce your death timer by 50%.
Reward: After collecting a total of 200 essence you no longer have a death timer and will re-spawn instantly.

Raptor: Enter stasis for 2 seconds and emerge a Raptor, increasing Leaping attack's range and damage by 100%. Leaping Attack will slow enemy heroes hit by 10% for 3 seconds. Killing an enemy hero within 3 seconds of hitting them with Leaping Attack will reset it's cooldown.

Tier 6:

Executioner: Attacking a Hero that is slowed, rooted, or stunned increases your Basic Attack damage by 30% for 3 seconds.

Evolved Armor: Gain 25 armor, reducing incoming damage by 25%.

Adrenal Infusion: Activating Zergling Aggression will apply its effects to nearby minions and mercs excluding bosses.

Tier 7:

8-Pool: Gain 7 zerglings instead of 5.

Primal Mutation: The damage bonus is increased to 50%.

Adrenal Glands: Permanently increases you and your allied zerglings' attack speed by 42.9%.

Swarmlings: Activating your trait will summon 1 extra zergling and your maximum number of zerglings is increased to 30.

Unstoppable Rush: Activating Metabolic Boost makes you unstoppable for the duration.

Strong Against:

Tracer: A nightmare for Tracer as he could rush her down and catch up with her even after she dashes away.

The Lost Vikings: If they split push, Tusky could pick them off one by one.

Li-Ming: He can seriously harass her due to his movement speed and her low health.

Chromie: Can burst her down quick but needs to be careful as she can do the same to him.

Raynor: He can push you away with his Penetrating Round, but apart from this he has no real way to keep you away.

The Butcher: With the right talent picks he won't be able to catch you without help, unless he catches you with a Lamb to The Slaughter.

Weak Against:

Arthas: Forget it. He has an AOE that will kill you and your allied zerglings and he reduces your basic attack damage.

Cho'Gall: He has so much health that even with an assassin spec you won't be able to burst him down.

Stiches: Too much health and his hook and gorge skills can decimate you.

Diablo: His CC and high health would be problematic for you.

KT: Although you could technically burst him down, one combo from him will end you.

Tyrande: You could burst her down but if she marks and stuns you, its over.

Xul: His shields, CC and large AOE damage will completely wreck you.

Zeratul: The one hero you should fear above all others.

Strong Maps:

Haunted Mines
Blackhearts Bay
Garden of Terror
Cursed Hollow
Warhead Junction

Neutral Maps:

Battlefield of Eternity
Tomb of the Spider Queen
Sky Temple
Infernal Shrines
Towers of Doom

Weak Maps:

Volskaya Foundry
Dragon Shire
Hanamura
Braxis Holdout

As you can see he would excel on maps that offer lots of roaming and ganking opportunities. Also he would be great on maps that have objectives that are spread out on large maps due to his mobility. However, due to his squishy nature and the need to be constantly on the move he would suffer on zone control objectives, which would in turn force him into a split push build and be unable to effectively help his allies control a point.