If you do, this attack does 120 more damage for each card you discarded in this way
Heatran GXs selling point is its ability Burning Road, a boosted version of Flash Fire that gives any number of Fire energies attached to other Pokmon to Heatran GX when it is moved from the Bench into Action
(There is a lot of room between "deck is good" and "not good enough for modern" - as in being the best choice, and giving you zero chance at victory
On top of that, Narset gives all your creatures prowess, so every spell you cast makes your team hit harder, meaning you can chain removal, card draw, or even extra combat spells right out of the graveyard while buffing your board
It does take a lot to get it to that point, but dropping three artifacts onto the battlefield can end the game
If the card is very expensive or will be very expensive at a GM10 grade, the grader will usually take more time looking at the card or even consult senior graders about the card