To begin with, early game Slark is essentially about as menacing as a paper napkin. Slark needs a pretty decent baby sitter to survive early game without heavy harassment. After Slark gets to level 6 things get trickier, but the fact remains that Slark has no survivability when faced with nukes.
So the effective counter heroes will deal heavy amounts of burst damage and essentially kill Slark before he has time to fully finish his combination of
shadow dance, and leech enough stat points through
While you may not always be able to team up to kill a hero, it is still recommended to try to wrangle at least 1 other teammate to assist. But given your criteria, and whether with support or without you will need to provide truesight. So wards, or dust if you intend on going 1 on 1.
Lina - unloading the early/mid game combination of her
light strike array,
dragon slave, and
Bane Elemental -
fiend's grip, follow up with another
brain sap - items to get in the mean time,
necronomicon so that the minions can pound away while you disable
Leshrac - between
diabolic edict and
pulse nova Slark will have a pretty hard time standing directly next to you or even using
pounce. On the off chance you are pounced on
split earth should be like shooting fish in a barrel to land. And you still have
lightning storm to cast.
Nerubian Assassin -
vendetta, attack, repeat whichever skill is done it's cooldown.
- observer wards
- sentry wards
- gem of true sight (situational)
- necronomicon - (upgrade this) minions for added dps and on-demand true sight
- blademail - synergy counter as
essence shift and damage incoming is redirected
- ghost scepter - disable Slark
- eul's scepter - disable Slark
- force staff - to break pounce link
- blink dagger - to break pounce link