I noticed this while testing, this happens only if you use a few Frosty towers with Frosty Power. If the enemy survives long enough until the end of the channeling and another frosty is close to the enemy, it can happen that another frosty will buff this frosty. Which can lead up to that the buffed up frosty can also buff up other frostys and so on. With that it is easily possible to reach hundred of millions or billions of damage on towers with well placed frostys.
Steps to reproduce:
Frostys don't buff other Frostys.