Considering tutors are often either setting up a winning turn or a desperate move to search for land, dropping an Opposition Agent at the right time can be stone-cold brutal
(2014-07-18) If enough -1/-1 counters are put on Chasm Skulker at the same time to make its toughness 0 or less, the number of +1/+1 counters on it before it got any -1/-1 counters will be used to determine how many Squid tokens you get
It can easily be the only Vehicle in your deck
Once Upon a Time was the most valuable card in pre-ban Selesnya Adventures, with most of the deck made up of commons, uncommons, and near-bulk rares
Force of Will is a big one, for example - copies from Alliances will set you back $65
If it tries to put an instant or sorcery card onto the battlefield this way, that card remains in its current zone instead