Mesmeric Orb

Whenever a permanent becomes untapped, that permanent's controller mills a card.

Sphinx's Tutelage

Whenever you draw a card, target opponent mills two cards. If two nonland cards that share a color were milled this way, repeat this process.
{5}{U}: Draw a card, then discard a card.

Ruin Crab

Landfall — Whenever a land you control enters, each opponent mills three cards. (To mill a card, a player puts the top card of their library into their graveyard.)

Psychic Corrosion

Whenever you draw a card, each opponent mills two cards.

Profane Memento

Whenever a creature card is put into an opponent's graveyard from anywhere, you gain 1 life.

Peer into the Abyss

Target player draws cards equal to half the number of cards in their library and loses half their life. Round up each time.

Mindcrank

Whenever an opponent loses life, that player mills that many cards. (Damage causes loss of life.)

Lord Xander, the Collector

When Lord Xander, the Collector enters, target opponent discards half the cards in their hand, rounded down.
Whenever Lord Xander attacks, defending player mills half their library, rounded down.
When Lord Xander dies, target opponent sacrifices half the nonland permanents they control of their choice, rounded down.

Syr Konrad, the Grim

Whenever another creature dies, or a creature card is put into a graveyard from anywhere other than the battlefield, or a creature card leaves your graveyard, Syr Konrad, the Grim deals 1 damage to each opponent.
{1}{B}: Each player mills a card. (They each put the top card of their library into their graveyard.)

Fleet Swallower

Whenever Fleet Swallower attacks, target player mills half their library, rounded up.