Linvala’s middle ability won’t trigger at all if you don’t have a full party as your combat phase begins. It won’t affect the target if you don’t have a full party as it resolves. The number of creatures in your party may change between these times, however.

The nonland permanent remains affected until your next turn even if the number of creatures in your party changes or Linvala leaves the battlefield.

Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keyword abilities (such as equip) are activated abilities and will have a colon in their reminder text. Triggered abilities (starting with “when,” “whenever,” or “at”) are unaffected.

No abilities of the affected permanent can be activated, including mana abilities.

In a multiplayer game, if you leave the game after Linvala’s middle ability resolves but before your next turn begins, its effect lasts until your next turn would have begun. It neither expires immediately nor lasts indefinitely.

To determine “the number of creatures in your party,” check whether you control a Cleric, whether you control a Rogue, whether you control a Warrior, and whether you control a Wizard. The number is the total number of those checks to which you answered yes. Each creature you control can be counted for only one of those checks.

If a creature has more than one party creature type, and there are multiple ways to count that creature that could result in a different number of creatures in your party, the highest such number is used. For example, if you control a Cleric and a Cleric Wizard, the number of creatures in your party is two. You can’t choose to have it be just one by counting the Cleric Wizard first as a Cleric.

An ability referring to the number of creatures in your party gets a number from zero to four. Such abilities never ask which creatures are in your party, and you never have to designate specific creatures as being in your party. You can’t choose to exclude creatures from this count to lower the number.

Some cards refer to you having a “full party.” This is true if the number of creatures in your party is four.