The above shows the initial cantrips and counterspells that best fit the deck. All of the modal cantripping options are included first to cement our wizards tools, and to exploit gandalf's copy ability. Same for the dfc card draw lands, which won't be factored in the 33 total. Next is the must include rhystic study. Two true tutors make the cut as they reinforce the dramatic reversal plan, act as cantrips, and the deck will essentially be a spell toolbox so super modal. They also are excellent copied. Following this is the most independently bang for our buck 1 mana cantriping instants. To make Gandalf good we must be able to activate as much as we want and when we want, and this requires a critical mass of cheap or free tricks as well as card advantage. our card advantage has to overflow as some amount of the time gandalf is going to take our draw from us, and we have to stay ahead of this. 1 mana cantrips straddle this line well, and as a base can offer 1 mana divinations when copied. Flavor wise it also shows the unpredictable nature and abilities of Gandalf. Incidentally we get 5 quality counterspells this way. The remaining cantrips depend if we want to maximize the most high value independent cards, or build into a graveyard theme.