This is the first time TPCi has banned cards outside their quarterly announcements:
A popular combo with Red Card, Delinquent, and Peeking Red Card created a lot of situations where one player essentially lost the game before taking their first turn. When this kind of strategy can be executed successfully a high percentage of the time and is effective, it creates an unhealthy environment.
Lusamine allows for an infinite cycle of Supporter cards because it can get back a different Lusamine plus another Supporter card. This has created several strategies that negatively affect the Expanded format. It can also create stalemate situations where neither player is able to win.