Masques block

The Masques block is the fifth block, consisting of the large expansion Mercadian Masques and the two small expansions Nemesis  and Prophecy. The block was released in 1999–2000.

Mechanics
This block included the searchable Rebels and Mercenaries, Spellshapers, new cards with alternative costs, and new abilities playable by any player (i.e. Squallmonger). It introduced the keyword Fading and Rhystic magic — discounted spells and abilities that work properly unless a specified player pays a set amount of mana.

Development codenames
On the development codenames for the Masques block, MTG.com columnist Mark Rosewater wrote: The Masques block was the beginning of codenames themed for an entire block. Why Greek names? While R&D was coming up with silly names, my girlfriend (now my wife) Lora (Rosewater) suggested the word Archimedes. Because we knew we needed a theme, we chose to follow up with two other Greek names. The reason that Greek names won out over another theme was that R&D thought it funny not only to have odd-sounding names that were themed, but also to choose words that the rest of the company would have trouble spelling.