Command Tower

{T}: Add one mana of any color in your commander's color identity.

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Counterspell

Dimir Cluestone

{T}: Add {U} or {B}.
{U}{B}, {T}, Sacrifice Dimir Cluestone: Draw a card.

Arcane Signet

Dark Ritual

Brainstorm

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

Dimir Signet

Lazav, Dimir Mastermind

Hexproof
Whenever a creature card is put into an opponent's graveyard from anywhere, you may have Lazav, Dimir Mastermind become a copy of that card, except its name is Lazav, Dimir Mastermind, it's legendary in addition to its other types, and it has hexproof and this ability.