Judge's Tower (Modified Rules I play by):

All players share the deck and a graveyard. You own every card you draw for purposes of things like Homeward Path.
Begin the game with 0 cards in hand.
You must play every card in your hand as soon as legally possible. All optional modes are mandatory, to the extent that you can fulfill them.
You must activate one ability of permanents you control once per turn as soon as legally possible. Always activate abilities from the bottom of the card up.
If a spell or ability has X in its mana cost, X is always 5.
You must attack with all legal attackers and Block with all legal blockers whenever the option is presented to you.
All players have infinite life.
All players have infinite mana.
You lose the round if you commit a game rules violation
You lose the round if you commit an illegal action (illegal targets, declare illegal attackers/blockers, etc.)
You lose the round if you fail to cast/activate something as soon as you could or miss a trigger you control
Play the game until someone loses, the other player gets a point. Remove from play all permanents the loser controlled, all cards from the loser's hand, all cards in the shared graveyard and all cards from shared exile.
After a point, resume play on the same players turn and at the same phase
The game is over when someone draws from the empty library, player with the most points wins!

Notes on individual cards:

Geth, Lord of the Vault: Ability is only activated if a MV 5 target is in the graveyard
Profane Memento: "Opponent's graveyard" counts when your opponent controls the ability/permanent/effect putting the card in the shared graveyard.
Tectonic Giant: Like with activated abilities, pick modal effects from the bottom of the card up
Conqueror's Galleon: Crew ability - can tap all of your creatures into the crew if desired
Liliana, Death Weilder - Opponent may choose to attack planeswalker or you
Approach of the Second Sun - If you win the game with this spell, you get a point and then loser exiles their board and play continues