Cold

Cold is debuff, that stacking up to 1000 times

Target losing 1 stack every 0.01 seconds (999 stacks = 9.99 sec)

Movement speed decreased by 0.1% per stack (999 stacks = 99.9% slow)

Fire and frost debuffs interaction
Applying 1000 stacks of Cold removing all stacks and applying 400 Ice

Applying Cold on target with Ice applying 40% of Cold stacks to Ice instead

Applying Ice on target with Cold removing Cold stacks and converts 40% of them to Ice

Applying Cold renews Burning to 5 seconds and reducing the Burning damage by 5 per stack applied

Target with Cold cant burn, removing 1 Wet for every 5 Burning applied, but reducing Burning for 5 damage per stack removed

Elementalist is very skilled in elemental magic and can apply Burning with Wet/Cold/Ice at the same time, without losing any stacks.