If I play Mirror Image on an enemy Darius, will it enter ready and +2?

No, your Reflection token will not enter ready with +2 Might.

Here is the breakdown of why this interaction functions this way:

1. Darius's Trigger: The ability on Darius, Trifarian ("When you play your second card in a turn...") is a triggered ability that specifically looks for you playing a card. A Reflection token created by Mirror Image is not "played" as a card; it is created by a spell effect. Therefore, it does not trigger Darius's ability.
2. Copy Effects and Buffs: Even if Darius's ability did trigger, Mirror Image creates a copy of the unit's base characteristics. Per the Riftbound rules (as noted in the related FAQs for Mirror Image), copy effects do not inherit temporary buffs, stat modifications, or bonuses currently applied to the original unit (Rule 375 and related FAQ #9410).
3. Entering Ready: Mirror Image explicitly instructs you to "Play a ready Reflection unit token." Your token will enter the board ready because the spell specifically tells it to, but it will not gain the +2 Might from Darius, and it will not gain the ability to ready itself further, as it is a Reflection token—not a copy of the Darius, Trifarian card itself that would trigger its own "played" condition.

In summary, the Reflection token will enter the board ready as per the instruction on Mirror Image, but it will not receive the +2 Might bonus.