Hi, so we have a Felidar Guardian in the graveyard and we use Animate Dead on it. When it enters we blink the Aura, so the Guardian dies, then we blink again the Aura that makes the Guardian ETB again in a infinite loop. Is this correct or does the "blinking" resolve in the stack before the Guardian goes in graveyard again ? Thanks in advance for the answers.

The SBA (state based actions) are only checked just before a player would get priority. In your example, they are not checked during the blink of Animate Dead, and as a result, when Animate Dead returns, the Guardian is not a valid target.

Sacrificing the Guardian before resolving the blink would not work neither, because then, the SBA would be checked before the blink, hence Animate Dead would be in the graveyard.

But with 2 x Guardian it works ! (-: