My opinion from a slightly different angle, I think this will create unnecessary tension between the DM and players. I'll explain -
All DMs here, no matter how good or bad, you know that deep down inside, you hate to see the players tear through a nicely crafted encounter. Sure, the game is your prime interest, but you want to keep the challenge up for the players, and eventually your own ego settles in and you start taking combat just slightly personally. Now add this mechanic to the equation. Each "side" now has a way of slightly (well, depends on the exact magnitude of these powers' effects) forcing the others hands. Now, as a DM, to which lengths will you go to save an encounter? Will you play dumb monsters smart? Will you play smart monsters dumb? Or even worse, will you plan ahead (assuming there are ways to make yourself immune to marking)? All this also applies to the players' angle, and for many players the game is competitive enough.
That's my opinion at least...
edit - By the way, I have no problem with the players creatively breaking my encounters on occasion, but this in not creative, this is round-to-round mundane abilities...
All DMs here, no matter how good or bad, you know that deep down inside, you hate to see the players tear through a nicely crafted encounter. Sure, the game is your prime interest, but you want to keep the challenge up for the players, and eventually your own ego settles in and you start taking combat just slightly personally. Now add this mechanic to the equation. Each "side" now has a way of slightly (well, depends on the exact magnitude of these powers' effects) forcing the others hands. Now, as a DM, to which lengths will you go to save an encounter? Will you play dumb monsters smart? Will you play smart monsters dumb? Or even worse, will you plan ahead (assuming there are ways to make yourself immune to marking)? All this also applies to the players' angle, and for many players the game is competitive enough.
That's my opinion at least...
edit - By the way, I have no problem with the players creatively breaking my encounters on occasion, but this in not creative, this is round-to-round mundane abilities...