therwise known as "Instants Matter Block" or "Timespiral 2.0"
~Color's Relationship with the Stack~
The stack obviously represents time, and colors treat it as such.
Blue - Blue enjoys playing with time, and thus manipulating cards on the stack. Blue doesn't really care much about the number of cards on the stack, however, and doesn't have much in the way of filling it up. However it can alter the way it progresses, and blue has had this ability ever since the classic counterspell.
Black - Black sees time as a weapon it can use against the opponent. Like blue, it doesn't care quite as much about the number of cards on the stack as other colors (though slightly more than blue), and instead prefers to hurt the opponent based on their relationship with time, i.e, the stack. This is flavorfully represented as black making things age quickly so as to harm them.
White - White, as the soldier's color, isn't quite as interested in the stack as other colors. However, as the army color, white knows that quick manuvers can be key in battle. Also, in its efforts to undermine black, it has effects controlling the stack and its power.
Red - Red sees time as something fun and powerful and thus likes seeing how it can use it to blow things up. Its a bit similar to blue in that it likes manipulation of the stack, however it isn't nearly as methodical about it and just likes throwing things at it. This randomness can get it in trouble sometimes (red has effects that can backfire if it is in the wrong position on the stack). Finally, Red considers time exciting and likes seeing just how big he can make that stack. The bigger, the more fun! In short, Red manipulates the stack like Blue, and grows the stack like Green, but does both in a rather haphazard but flashy manner.
Green - Green sees time as a natural force and thus a force that should be protected and nurtured. As such, green grows the stack like red, only much more carefully. Green also seeks to protect the stack from manipulation at the hands of Blue, Black, and to an extent, White.
Flash - This is incredibly key to the block. All colors have many cards with flash, with slightly less in white.
Affinity for Spells (For each spell on the stack, this card costs less.) - All colors have some of this keyword, though blue has less because it cares more about the manipulation of time than the amount of it which passes.
Warp [cost] (While this card is on the stack, you can pay [cost] and put this card on top of the stack.) - This is Blue's favorite keyword, and Black and Red like it too. None in green, at all.
Timebind - [effect]. This is not technically a keyword (its something like landfall). It does an effect (generally negative) to each player with a spell beneath it in the stack, once for each spell beneath it in the stack.
Instant Tokens - They are alive only while on the stack, and removed immediately afterward. Some spells are "split" into two effects, making them harder to counter and such, and helping grow the stack.
1. Stacklands. A cycle of lands like the one below:
Land - Island
: Put 1 Instant Token with "Add to your mana pool" on the stack.
2. The Cycle Representing Each Color's Relationship
Spells are placed on the bottom of the stack when cast rather than on top.
No more than 1 spell can be on the stack at a time.
The first time you cast a spell each turn, each player must discard 1 card for each spell they control under it on the stack.
The first time you resolve a spell each turn, deal x damage to target creature or player where x is the number of spells you control on the stack.
During each upkeep, put two Instant Tokens on the stack with "add to your mana pool."
Potential? Mechanic updates? Card ideas? Fixes?