Unless youre in possession of an obviously rare and desirable card, the amount of money you spend shipping a card and having it graded is rarely going to be worth the amount youll sell that card for on the secondary market
You can try to cut it and play those lands instead: 1 Gemstone Mine (the first one is acceptable, but sucks in multiples), 1 Spirebluff Canal and 2 additional fetchlands
While these three archetypes do have plenty of overlap, its easy to build distinct decks supporting each theme
Have you thought about what happens when you cast Self-Destruct on Screaming Nemesis
So rare, in fact, that theres no really any information about where it came from
Kroxa works quite well with other discard and aristocrat effects, so if this giant is your commander, load up on cards that take advantage of these effects