League-of-legends – HARD counter to Riven

It is a good buy versus anyone who has ultimates or abilities that rely on health regeneration.

The active makes this item extremely effective against champions with healing abilities, as well as the use of health potions. It is also effective against champions and item builds that rely on spell vamp and/or life steal.

Examples of champions/abilities/items that it counters include:

• Health Potion
• Dr. Mundo's Sadism
• Fiddlesticks's Drain
• Soraka's Astral Blessing and Wish
• Swain's Ravenous Flock
• Warwick's Hungering Strike and Infinite Duress
• Sion during Cannibalism
• Tryndamere's Bloodlust
• Renekton's Cull the Meek
• Volibear's Chosen of the Storm
• Vladimir's Transfusion
• The Bloodthirster / Sanguine Blade
• Summoner Heal

Source

So, if there is particularly abusive Swain, Warwick, or Sion then it can help stop them.

To specifically counter Vladimir you should choose a champion with some or all of the following tools in their kit:

• A gap closer (If Melee)
• Burst Damage
• Crowd Control.

By selecting a champion with two or more of these tools you will be able to pressure Vladimir into using his pool which uses a considerable amount of his health. By pressuring him early and often you will deny him farm which delay his very strong late game presence.