Black Market (Abcdefghijklnmp's version)

The Black Market is a new mechanic added in a yet unidentified version of BTD games. Its mechanics are very different from other shops; its main currency is lives (something which almost nothing uses), and behaves very differently.

Mechanics
The market has two sections: Basic, and Premium. All Basic trade slots (trade slots are slots which show trade deals that you can make) will always be available but will be swapped out for another trade deal once you purchase the current trade deal. However, Premium trade slots are mostly locked at first. Each empty Premium trade slot has a chance of offering a trade deal after you purchase a Basic trade deal. There are 5 Basic slots and 6 Premium slots.

Premium slots are further divided into 3 groups: Silver, Gold, and Platinum. There are 3 Silver slots, 2 Gold slots, and 1 Platinum slot. Each of them are equally likely to offer a trade deal, but because of their number you are more likely to get a Silver trade deal than a Platinum one. They also differ in value.

The main currency is lives. Thus, deals of the same price may differ in value across different difficulties and vice versa. A deal asking for 5 lives in exchange for a permanent speed up in Sabotage Supply Lines may be more effective in Hard and less effective in Easy, and reduce the cooldown to 0 in Impoppable.