All Primary Monkeys in radius get tier 1 upgrades for free.
N/A (except 4/1/0 and 4/2/0)
+10% range, affects nearby towers
+15% attack speed, affects nearby towers +10% additional range, affects nearby Primary Monkeys +1 pierce, affects nearby Primary Monkeys +15% (?) projectile speed, affects nearby Primary Monkeys Grants free Tier-1 upgrades, affects nearby Primary Monkeys
Restricted (can be upgraded to grant camo detection as 4/2/0)
Primary Mentoring is the fourth upgrade of Path 1 for the Monkey Village in BTD6. It allows all Primary towers within its radius to be granted free tier 1 upgrades. It costs $2125 on Easy, $2,500 on Medium, $2700 on Hard, and $3000 on Impoppable.
This upgrade benefit alone is best used with Bomb Shooters, as their Tier-1 upgrades collectively are the most expensive of their kind.
Primary Mentoring can be useful as a method of verifying that a Primary Monkey is benefited by Primary Training upgrade bonuses, since only Primary Monkeys are affected by both upgrades.
Primary Mentoring as seen in the upgrades menu
Primary Mentoring upgrade icon
Primary Mentoring Crosspaths (Top: Path 2, Bottom: Path 3)
The most expensive upgrade that can purchased for free with Primary Mentoring is the Bigger Bombs upgrade from the Bomb Shooter, saving $400 on Medium each.
The most expensive combination of upgrades that become free by the Primary Mentoring benefit is the Bomb Shooter with Bigger Bombs and Faster Reload, totaling a saving of $650 on Medium each.