2016-09-20 : For a spell with {X} in its mana cost, use the value chosen for X to determine its mana value. For example, Clash of Wills is an instant spell with mana cost {X}{U}. If you chose 2 as the value of X, then Clash of Wills has mana value 3, and Metallurgic Summonings's ability will create a 3/3 token.

2016-09-20 : If Metallurgic Summonings's first ability resolves and the spell that caused it to trigger has been countered, use that spell's mana value as it last existed on the stack to determine the value of X.

2016-09-20 : Metallurgic Summonings's first ability resolves before the spell that caused it to trigger.

2016-09-20 : The number of artifacts you control is checked only as you activate Metallurgic Summonings's last ability. It's not checked again as it resolves.