Soul's Might Mirari copy sorcer spell for +1/+1 counters?

[Swamp]

If I cast Soul's Might on a creature with power 2
and I copy the souls might with Mirari

Does the creature end up getting 4 +1/+1 counters or 6 or 8?

[Kenji]

Soul's Might will look at the creature's power as it resolves, and that determines the amount of +1/+1 counters the creature will get.

So, in the scenario you provided, your creature would end up with 6 +1/+1 counters. The Mirari copy of Soul's might resolves first, giving the creature 2 +1/+1 counters. Then the original Soul's Might resolves, giving the creature 4 counters (since its power is now 4).