If the discarded card is an artifact card, it will be counted as you determine the value of X, provided it's still in the graveyard or, optimistically, on the battlefield under your control at that time
These ever changing formats dont allow you to rely on professionals to build your decks for you, they make you do all the work
For each generic mana in that cost, you may tap an untapped artifact or creature you control rather than pay that mana. 701.67b: If a waterbend cost is part of the total cost to cast a spell or activate an ability (usually because the waterbend cost itself is an additional cost), the alternate method to pay for mana described in rule 701.67a may be used only to pay for the amount of generic mana in the waterbend cost, even if the total cost to cast that spell or activate that ability includes other generic mana components
Sheoldred is good against the mirror in theory as its a haymaker, but mana is a concern
Anim Pakal, Thousandth Moon Anim Pakal, Thousandth Moon is a powerful token generator that happens to be a soldier