With the 'mechanics' mentioned in the previous three weeks, there may well be particularly well known games that we automatically associate with those mechanics, but they have appeared so consistently as to stand alone, conceptually, as a 'mechanic'.
Role selection is, doubtless, such a 'mechanic' too, but I suspect discussion this week will necessarily be inspired by one particular game, and I doubt we would have thought of this topic for the series had Puerto Rico not been such a success within the boardgaming hobby. Equally, I would suggest that 'role selection' seems to be a relatively new mechanic in games, and so I've just outlined the 5 games that, to my knowledge, are the only ones to feature 'mid-game role solection' (as opposed to varying abilities provided to specific players for the duration of a game, as seen in Cosmic Encounter et. al.).
Looking at it mechanically, role selection involves players picking a particular role for a turn (or other segment of the game), which will give them new abilities and/or weaknesses while they hold that card. Typically, this is done by either drafting "roles" from an open selection, or passing around cards from which players pick a role when the cards reach them. The differences between 'open' and 'hidden' role selection is probably something we might like to discuss.
Naturally, the order of picking roles will be an issue, particularly if (as seems wisely the case) there is a limit on how many times a certain role can be picked. Also, especially in hidden role selection, where player no.2 ought not to have perfect information about what playe no.1 picked, it may be that some of the roles are randomly removed from those available in any given turn.
Getting to the specific games that use this mechanic, I can only find, as I said, 5 (and two of these are semi-sequels). Notably, they are all games that have recieved a reasonable degree of critical acclaim (to a greater or lesser extent, for sure, but few would argue any were failures).
Verrater and Meuterer, both by Marcel-Andre Casasola-Merkle, are arguably the first role selection games. In these clever card games (often described as board games packaged as card games), players secretly selected roles that would influence, in the respective games, a medieval civil war or the fortunes of a ship's crew. In both games, selection of roles will potentially divide the players into two groups against each other.
Bruno Fadutti's Citadelles (aka Ohne Furcht und Adel) uses a similar role selection to decide the turn order, as well as giving special abilities.
Puerto Rico and San Juan are the most commercially and critically successful examples. In both, the roles trigger activities by all players, but with the role selector recieving some sort of bonus. This role selection mechanic is thus particularly interesting for tying phase order to special ability selection.
Anyway... enough of me. Have I missed any games? Is this a "new" coremechanic that will be rapidly utilised elsewhere, or an interesting one that will just not see the ammount of use auction mechanics get?
Richard.
What about Maharaja?