i was just playin a game right now and tbs rain of ice negative effect does nothing. Its just so useless coz of how long it lasts on its first 2 levels.
early game, everyone has very slow attack rate anyway, so the negative effect on lvl 1 only effects a target for basically 1 attack.
i think that the time needs to be the same through out all lvls of this skill but the effectiveness (%) continues to increase with each lvl.