Drowner Initiate

Whenever a player casts a blue spell, you may pay {1}. If you do, target player mills two cards.

Counterspell

Return target nonland permanent to its owner's hand. Each player mills two cards.

Flying
Jace's Phantasm gets +4/+4 as long as an opponent has ten or more cards in their graveyard.

Whenever you draw a card, you may have target player mill a card.

Whenever another snow permanent you control enters, you may have target player mill two cards.

Bojuka Bog enters tapped.
When Bojuka Bog enters, exile target player's graveyard.
{T}: Add {B}.

Target player mills a card.
Draw a card at the beginning of the next turn's upkeep.

Draw three cards, then put two cards from your hand on top of your library in any order.

Return target nonland permanent and all other permanents with the same name as that permanent to their owners' hands.

Target player mills two cards.
Draw a card.

Target player mills X cards, where X is the number of lands you control.

Each player discards any number of cards, then draws that many cards.
Draw a card.