Cryo Cannon is the third upgrade of Path 3 for the Ice Monkey in BTD6. It allows the Ice Monkey use a freezing cannon to shoot freezing snowballs. This will replace its freezing cold radial blasts with a projectile freeze attack fired at a faster rate (2.4x faster, shoots every 1.0 seconds) with less pierce (30 as opposed to 40) and a smaller blast radius. Along with this replacement attack is significantly extra range for the Ice Monkey to shoot snowballs at further range. It costs $1,700 on Easy, $2,000 on Medium, $2,160 on Hard, $2,400 on Impoppable.
This upgrade will improve the Ice Monkey on places where maximum track area is problematic, such as where there are poor track bends around the entire track. On the other hand, it makes the tower worse than not having Cryo Cannon if placed where there are poor spaces for optimizing straight lines.
On most cases, it is worse than a x/x/2 Ice Monkey, due to the relatively low pierce and tiny blast radius. However, there are some useful cases where Cryo Cannon can be better than a x/x/2 Ice Monkey, such as being able to catch Super Ceramics a lot more effectively.
Since the Cryo Cannon upgrade is at least twice the price of a single 0/0/2 Ice Monkey and just under the price of a 0/1/2 Ice Monkey, it is generally more worth purchasing two x/x/2 Ice Monkeys rather than one x/x/2 Ice Monkey.
With Cryo Cannon, there is more control over what nearby bloons should be or shouldn't be frozen. Particularly with the new target priorities: First, Last, Close, Strong.
The Cryo Cannon upgrade currently costs as much as the Ice Shards upgrade did in BTD5. Interestingly, the BTD5 Absolute Zero upgrade following the BTD5 Ice Shards upgrade also costed the same, at a cost of $2000 on Medium.
In Version 2.0, the Ice Monkey got a buff to the base freeze pierce. This did not affect Cryo Cannon or its subsequent upgrades, but it did affect all other Ice Monkeys.