Executive Meddling: Tetris: The Grand Master ACE. The Tetris Guideline, a series of rules that games carrying the "Tetris" name must abide by, forced significant changes to the gameplay mechanics. On top of that, Microsoft wanted Arika to hurry the game to make it a launch title for the Xbox 360 and incorporate downloadble content; as a result, proper ARS can only be unlocked if you have an XBL Gold account.
Arika has, on two occasions, had videos of TGM clones (such as Heboris and Texmaster) removed from YouTube. In the case of the second wave of removals, Arika denied doing so of their own volition, claiming that The Tetris Company made them do it, which leads to some Unfortunate Implications about TTC's possible intentions. Since then, most, if not all, videos of TGM clones have been put back up, with no further action from Arika or TTC.
TGM4 was allegedly canceled due to difficulty with "cleaning up foreign clones". Excuse me?