Metal Freeze (damage type)

Metal Freeze is a damage type introduced in the very first Bloons Tower Defense, and appeared in most games in the series. It is defined as the damage type unable to damage White Bloons and Frozen Bloons, but can damage any other type of Bloon, especially Lead Bloons. It was one of the first three damage types introduced in the series, the other two being Sharp and  Explosion. The Bloons Wiki represents this damage type with, the Bloons TD 6 upgrade icon for the Cold Snap upgrade (formerly named Metal Freeze), which grants this damage type.

This damage type has long been primarily associated with the Ice Monkey's various incarnations.

Bloons Tower Defense
The damage type was introduced in Bloons Tower Defense. It was the default damage type for the Ice Ball and was intended to provide a disadvantage to using freezing to stall Bloons from moving, since White Bloons and already-Frozen Bloons could not be stopped this way. Ice-based damage would continue to work this way until BTD5.

Bloons TD 5
Unusually, this damage type was completely absent from Bloons TD 5 Flash and its other Flash spin-offs. In its place, Metal Freeze/Glacier served as the Ice Monkey's default damage type.

Bloons TD 5 Mobile and Bloons Monkey City Mobile restored Metal Freeze as the default damage type for Ice Monkeys.

Bloons TD Battles
Bloons TD Battles Flash followed Bloons TD 5 Flash's lead and replaced Metal Freeze with Metal Freeze/Glacier.

Bloons TD Battles Mobile initially followed Bloons TD 5 Mobile's reinstatement of Metal Freeze, but update 3.5 changed it back to Metal Freeze/Glacier.

Bloons TD 6
Instead of reinstating Metal Freeze as the default damage type of the Ice Monkey, as BTD5M had done, Bloons TD 6 switched that to Cold, which cannot pop Leads by default. However, Metal Freeze damage could be purchased back with the Cold Snap upgrade.

Bloons Adventure Time TD
Bloons Adventure Time TD had Metal Freeze as the default damage type for its Ice Monkeys, just like BTD5M. This meant that Ice Monkeys could not refreeze Frozen Bloons. However, its Snap Freeze upgrade was Metal Freeze/Glacier and could damage frozens.