Rule of 6
The Rule of 6 is an informal game term, as opposed to the actual game rules of Rule of 4 and Rule of 9. While the Rule of 9 dictates that no more than 9 Free Peoples companions are allowed to be in play at a time, the practical limit is somewhere below 6. This is due to the existence of Shadow cards like Úlairë Enquëa, Lieutenant of Morgul (1U231) and Greed (1R125) which harshly punish Fellowships of 6 or more companions. The mere threat of the ubiquitous "Shotgun Enquea" and friends are a powerful enough deterrent that the savvy player won't casually violate this limit.
This is however a 'rule of thumb' and not a hard and fast game rule. If you can weather the setbacks from these Shadow cards, you can simply carry on with a large Fellowship (as is often done with Ent decks). Also, while most Shadow cards of this sort target six or more companions, some instead spot five or more (e.g. Savagery to Match Their Numbers (1R139) and Pitiless Orc (12U99)) and a few spot seven or more (e.g. The Number Must Be Few (1U260)).
Threats are another soft deterrent to letting the Fellowship grow too large, because your threat cap is the same as the size of your Fellowship. Cards that spot five or more threats, such as Mûmak Commander (7R152), are also quiet Rule of 6 cards.
The Rule of 6 was an intentional convention pushed by Decipher and not an emergent property. The design logic was that since both players refill their hands to 8 cards, then a full Fellowship of 9 companions on the table would make the Ring-bearer untouchable at all times for skirmishes, even if the Shadow player had a rare perfect hand made of exactly 8 (affordable) minions. Thus, cards targeting a 6-companion limit pump the brakes on truly large Fellowships and bring it down to a level that's more manageable with only 8 cards in hand.
- Úlairë Enquëa, Lieutenant of Morgul (1U231)
- Greed (1R125)
- Isengard Smith (3U60)
- Southron Commander (4U249) and Southron Troop (4R256)
- Mûmak Commander (7R152)
- Morgul Squealer (8R77)
- Unending Life (12C181)
- Úlairë Cantëa, Black Assassin (12R174)
- Vengeful Wild Man (17C63)