
Here are the cards:
Interstellar Migration (TkatG)
Keeper of the Great Library (TKatG)
Alternative Historian (SoK)
Note that Alternative Historian has an action that can be triggered in any phase, and Keeper's ability does not stipulate that the yithian card entering the discard must come from play. This allows you to discard as many cards as you want with the Keeper in play and go through your whole deck, until you get all 3 of your Interstellar Migrations in the discard and a bunch of yithians (you only need 14 in the discard) to mill your opponent.
It seems apparent that this was overlooked by design and playtesting. When you have cards with no effective cost, and with no effective limit, it's only a matter of time until someone finds a way to abuse it. This was my worry when I heard that this expansion would have effects trigger-able in the discard (which is effectively untouchable by your opponent). When there is no ability to interact that leads to dangerous situations in terms of abuse of card effects.
So, what are your thoughts?
Restrict them to prevent the combo together? Errata one or both? If so, what should the errata be?