Cast Maddening Cacophony with kicker by paying , causing each opponent to mill half their library, rounded up.
Activate Consuming Aberration by tapping it, causing a opponent to mill cards equal to the cards in opponents' graveyards, milling the remainder of their library.

Cast Traumatize by paying its mana cost, causing an opponent to mill half their library, rounded down.
Activate Consuming Aberration by tapping it, causing the opponent to mill cards equal to the cards in opponents' graveyards, milling the remainder of their library.

The opponent will mill the remainder of their library unless each opponent's graveyard was empty when the combo started and the opponent had an odd deck size.

Declare Fleet Swallower as an attacker, triggering its ability, causing an opponent to mill half their library, rounded up.
Activate Consuming Aberration by tapping it, causing the opponent to mill cards equal to the cards in opponents' graveyards, milling the remainder of their library.

Declare Terisian Mindbreaker as an attacker, triggering it, causing the defending player to mill half their library, rounded up.
Activate Consuming Aberration by tapping it, causing the opponent to mill cards equal to the cards in opponents' graveyards, milling the remainder of their library.

Cast Overture by paying its mana cost, causing an opponent to mill half their library, rounded down.
Activate Consuming Aberration by tapping it, causing the opponent to mill cards equal to the cards in opponents' graveyards, milling the remainder of their library.

Declare Lord Xander as an attacker, triggering its second ability, causing the defending player to mill half their library, rounded up.
Activate Consuming Aberration by tapping it, causing the opponent to mill cards equal to the cards in opponents' graveyards, milling the remainder of their library.