Also, since Shoal Cave seems to be the Ice Type location, if they are there, specify low or high tide, also, what time is it considered low and high tide in the game?
As for the ice-related item, three great options are the Casteliacone (found in the Trick House), a Never-Melt Ice (found in Shoal Cave) or an Icy Rock (found at the Weather Institute).
Source
High tide is from 9 am to 3 pm and 9 pm to 3 am. Low tide is from 3 am to 9 am and 3 pm to 9 pm.
Hope I helped!
