Does Master Yi's leader effect need to be declared as a trigger to give an alone unit +2 might?

Ruling: No, Master Yi's effect does not need to be declared as a trigger because it uses "while" wording, making it a passive ability that doesn't use the chain.

Nuances:

• Effects with "when" wording (like Mask of Foresight) are triggered abilities that must be declared and go on the chain
• Effects with "while" wording are passive abilities that apply automatically without declaration or using the chain