23 Jun 2020
Because Experimental Overload is still on the stack while it's resolving, it doesn't count towards the value of X.
23 Jun 2020
The value of X is determined only as Experimental Overload resolves. The Weird's power and toughness don't change if the number of instant and sorcery cards in your graveyard changes.
23 Jun 2020
You exile Experimental Overload even if you don't return a card to your hand.