Sigma, Fractured Star

Double Strike, Flying
When Sigma, Fractured Star enters the battlefield, create a 0/4 Barrier token with Defender.
{t}{2}{u}, Any damage dealt to Sigma, Fractured Star until the start of your upkeep gets added to his total toughness. Activate as an instant.
Ultimate (When this creature deals non-ultimate damage, put that many Ultimate counters on it.)
{2}{u}{u}{u}, 20 Ultimate counters: Deal damage to all creatures an opponent controls equal to half of their total toughness rounded down. Activa