Eclipse

423.1.a.1. A Stunned Unit can not be Stunned again. Example: Eclipse Herald has the ability "When you stun an enemy unit, ready me and give me +1 [M] this turn." Its controller plays a spell that reads "Stun a unit." They may choose a unit that's already stunned, but if they do, Eclipse Herald will not trigger.

477.3.c. Players cannot increase a numeric attribute by a negative amount. If an effect would instruct a player to do so, they increase it by 0 instead. Example: A player plays Last Stand, which reads "Double a friendly unit's Might this turn. Give it Temporary." The player declares a 2 [M] unit as the target during finalization. In reaction to Last Stand, an opponent plays Eclipse targeting the 2 [M] unit. When Last Stand resolves, the unit is -2 [M]. Last Stand instructs its controller to increase the unit's Might by its current amount, -2, when the double action is performed. This is not possible, so the unit's Might is increased by 0 instead.

758.2. If the spell or ability changes for any reason such that it will no longer fall under the category of spells or abilities for which a Game Object is untargetable, the Game Object will become a legal target for that spell or ability. Example: A 1 [M] unit reads "I can't be chosen by enemy spells or abilities with Energy cost less than my Might." That unit is targeted by an enemy Falling Star; in reaction to the Falling Star, the unit's controller plays Discipline targeting that unit, bringing its Might to 3 [M]. If Falling Star resolved at that point, the unit would be unaffected by it as it resolves. Falling Star's controller plays Eclipse before Falling Star resolves, bringing the unit's Might to -1 [M]. When Falling Star resolves now, the unit is affected by the spell and has 6 damage marked. It dies in the following cleanup.