1 deck. Average. 2 redeals.
Only the top card of each pile is available to play. The piles are built down in sequence in suit. Only one card at a time may be moved. If you move all cards from a pile it cannot be resumed.
When you have made all the moves initially available, click on the empty stock pile to restack cards. During restacking all the remaining cards are first gathered together and dealt out into tableaus with 3 cards in each. If the last tableau contains 3 cards it's divided into 2 piles with two cards in the first pile and one card in the second pile.
You have two redeals.
Trefoil Solitaire is one of the games included into the BVS Solitaire Collection.