I found an (almost) solution to this. But we would need someone to modify an excisting script.
You can do this very easily with the
region common event script

I made a mini map with ice on it, and filled the ice with the region 63
Then, as the script required, I put the note in the note box of the map: regevt: 63 on 123
and in the common event 123 I made the next defined movement route:
This made that the player move forward 2 steps without the walking animation, so it looks like is slippering, and slowing it speed.
THE PROBLEM:
The script call again for the common event if the player moves to a region even with the define movement route command, so if the entire ice is filled with that region, it will just go forward until it's out of the region.
the only provisional way I could find to do this, is to make just some tiny tiles to be slippery and to try that they don't connect between them.
If someone is skilled enough, maybe they could modify the script to not call for a common event if the movement was made by the "define movement route" command.