The goal of this deck is to stall out any aggression with your walls and high toughness creature spells until you get High Alert. Out of nowhere you can have 3/3, 4/4, 5/5 and 6/6 creatures to swing in with. Tetsuko Umezawa, Fugitive makes them all unblockable, because they still have 0 attack, they are just assigning damage based on their toughness.

Card choices:

High Alert: The deck centres around this card. You want this in your opening hand if possible. You can win the game in a few turns while it's in play, or drop it and Tetsuko on the same turn for a massive surprise swing to the opponents face. The secondary effect of allowing you to untap a creature allows you to continue to block after your big swings.

Tetsuko Umezawa, Fugitive: Makes all your creatures unblockable because they still have 0 or 1 attack.

Surge Mare: Early "wall" that lets you cycle cards so you can look for your High Alert, as you can attack with it early.

Chemister's Insight: Draw so you can dig for your High Alert. Works well with Surge Mare as you can put it in the graveyard and still use it. You can substitute Sphinx's Insight if you feel you need more life gain.

Wall of Mist: A cheap wall. There is nothing special about this until you have High Alert in play, then it's suddenly a 5/5.

Senate Courier: A high toughness flyer. Allows you to go over opponents if you haven't found Tetsuko yet, and allows you to block in the air.

Amaranthine Wall: An indestructable wall. One your opponent sees your game plan they will try to remove your walls. This helps against that.

Absorb: A counter spell that gains you life. It's useful in most matchups, but can be substituted for any counter spell.

Azorius Knight-Arbiter: Late aggression. The unblockable is useful if you haven't found Tetsuko yet. You can also chip away at them if you haven't found High Alert yet while still having a good blocker thanks to Vigilance.

Deputy of Detention: Removes any non-land permanent from play. Great for dealing with enchantments and creatures, but particularly tokens as it completely wipes them all from the board.

Quench: Great early counterspell. Its usefulness wanes in the late game, but still good in a pinch if the opponent taps out.

Sideboard:

Negate: Swap this in for control matchups.

Ixalan's Binding: Something to deal with Planeswalkers and Niv Mizzet.

Seal Away: For aggressive creature strategies.

The Immortal Sun: More planeswalker hate. Me wary of attacking with your 1/X creatures while you have this out as they are no longer blockable with Tetsuko.

Settle the Wreckage: Bring it in for wide board strategies.

Shalai, Voice of Plenty: For aggressive spell strategies such as Mono Red and Rakdos. In most cases they need to use 2 spells to remove it, protecting your face. Also protects your Deputy of Detention. This can be main boarded if you like over Azorius Knight-Arbiter as there's currently a lot of aggressive spell based decks.