Soulbind

This upgrade has been replaced by the Prince of Darkness upgrade on July 23, 2018 (version 2.0) and no longer exists.

"Bind as many souls as you dare to the Wizard and it just might save your life..."

- BTD6 description

Soulbind was the final upgrade of Path 3 for the Wizard Monkey in the initial release of Bloons TD 6, and formerly the Tier 5 upgrade of Path 3 for said tower. Soulbind provided a new ability that allowed the player to bind as many towers as they wished to sacrifice them for extra lives if the player lost all their lives.

It costed $20,400 on Easy, $24,000 on Medium, $25,920 on Hard, and $28,800 on Impoppable.

It was replaced by Prince of Darkness in Version 2.0.

Sacrifices
Upon purchasing the tower, the Soulbind ability would be unlocked and its icon would appear in the ability interface. To Soulbind a tower, the player would tap the Soulbind ability icon, bringing up the prompt "Select a Tower to Soulbind", displaying a target reticle over any tower available to be Soulbound. Upon sacrificing a tower to Soulbind, the tower would be surrounded in a green aura for a short time and a sprite of a green skull would appear above the tower. At any point if the players life count were to dip below zero, any Soulbound towers would be sacrificed in exchange for lives, removing the tower from the map and increasing the players life count.

The Soulbind ability had a cooldown of 10 seconds.

The amount of lives gained from Soulbind depended on the monetary value of the towers; a higher value would result in more lives gained from a sacrifice. When a tower was sacrificed, you would get one life for every $100 sacrificed in financial value.

Trivia

 * Soulbind attacked at the same speed as Necromancer: Unpopped Army, unlike the replacement Tier-5 upgrade Prince of Darkness.
 * Soulbind's concept would later be incorporated into Adora's Blood Sacrifice ability, but in her case it sacrifices towers for hero XP.
 * This is the only upgrade removed from BTD6.
 * This upgrade was the first instance of a tower having an Activated Ability in its Bottom Path, the second being Dark Knight and its upgrades.
 * The first removed upgrade is not Soulbind but in fact Energy Beacon, a former upgrade for the BTD5 Monkey Village that was a Tier 3 upgrade that granted only reduced ability cooldowns.
 * According to this post, Ninja Kiwi stated that they scrapped Soulbind due to its unplayability and poor potential for improvement, so they started over and replaced it entirely with Prince of Darkness, which instead improves its undead bloon attacks.
 * Arguably, the Version 1.0 Wizard Lord Phoenix can be seen as even more useless than Soulbind due to its slow ability exchanging the Wizard itself for a transformed phoenix with the power of only a few Phoenixes plus a slow spray of 4 meteors, all for the cost of a hefty $80,000 on Medium.