Heat tipped [cis] darts allow popping of Frozen and Lead Bloons.
~ BTD6 description

BTD6 official artwork

Heat-Tipped Darts is the second upgrade of Path 2 for the Monkey Sub in BTD6. It allows the Monkey Sub to pop Frozen and Lead Bloons. This upgrade costs $255 on Easy, $300 on Medium, $325 on Hard and $360 on Impoppable.

This upgrade will give the Monkey Sub red paint near the front of the sub, underneath the gun, as shown in the artwork. Purchasing Path 1 upgrades will give the sub a green cap and green-lensed binoculars. Purchasing Path 2 upgrades will give the sub two guns, as well as yellow paint around the window on the side of the sub.

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