Heart of Vengeance

"Gains 10% attack speed and 1% for every life lost from the starting value after the upgrade. Maxes at 100% and diminishes if lives are restored."

- In-game description

 is the second upgrade of Path 3 for the Druid in Bloons TD 6. It gives the Druid automatic 10% attack speed, and adds a 1% attack speed buff for each life lost from when the upgrade is bought. The attack speed buff is capped at 100%, meaning that the maximum attack speed buff is attained when 90 net lives are lost. This buff will reverse if lives are gained. The upgrade does not consider any lives above the original amount of lives.

Secondary attacks such as Lightning from Heart of Thunder are also affected by this meaning they are cast faster.

It costs $255 on Easy, $300 on Medium, $325 on Hard, and $360 on Impoppable.

Appearance
TBA

Summary
Heart of Vengeance allows the Druid to become more effective in combination with life loss. For the best results, try juggling between losing as many lives as possible in the early-game and avoiding losing the game. In addition, avoid any life-regeneration upgrades in the defense, as this will harm Heart of Vengeance's special life-loss benefits.

An interesting strategy on game modes other than Impoppable or CHIMPS is to spam as many 0-0-2 Druids as possible and lose as many lives as possible without losing the game, allowing as many Druids as possible to benefit from this upgrade. Similarly, slowly using Ezili's Sacrificial Totem every so often to drain away lives manually can be done to create a similar effect.

On Impoppable and CHIMPS, this is simply a +10% attack speed boost, which while small is significant for already powerful Druid upgrades.

Tips

 * Just as losing lives will increase attack speed, gaining lives will make Druids with this upgrade attack slower. It is best not to use life gaining strategies with this path of upgrades, such as with Benjamin, Support Chinook's Supply Crate ability, the Spirit of the Forest upgrade, or Marketplaces with Healthy Bananas.
 * However, in practice, this effect is not as pronounced as the following upgrades can still be functional without the attack speed buff.
 * Lives absorbed by the Mana Shield do not count towards the attack boost.
 * Note that using a Continue will decrease Heart of Vengeance bonuses, as using a Continue gains lives, thus lowering Heart of Vengeance bonus.
 * On CHIMPS, since lives can neither be regenerated nor lost, treat this upgrade as just a +10% attack boost. It's a small boost, but it can make a difference for powerful Druid upgrades.

Trivia

 * Heart of Vengeance used to be useless on CHIMPS Mode, but has since changed after Version 9.0 by providing +10% bonus attack speed by default.
 * Similarly to Druidic Reach, the Heart of Vengeance's gem resembles the Plumbob from the Sims series. The Druid's gem is red, depicting anger.