Not a basic land, mind, any forest of plains
Hexmage also goes great in a sacrifice build
Legends : The First Set WithLegends Legends Obviously enough, the sets name clues you in on the importance of Legends in the set

Mono-Black Graveyard Baron Helmut Zemo 1.7%inclusion 35 decks 2.02K decks Ultron the Annihilator 3.5%inclusion 26 decks 753 decks Songbird, Sonic Screamer 1.5%inclusion 11 decks 753 decks Doctor Doom, Unrivaled 0.7%inclusion 5 decks 753 decks Liliana the Repentant 2.8%inclusion 4 decks 142 decks Top Commanders Imotekh the Stormlord 12%inclusion 375 decks 3.15K decks Syr Konrad, the Grim 6.0%inclusion 189 decks 3.15K decks Sephiroth, Fabled SOLDIER 5.8%inclusion 137 decks 2.35K decks Xu-Ifit, Osteoharmonist 5.8%inclusion 132 decks 2.27K decks Liliana, Heretical Healer 3.5%inclusion 110 decks 3.15K decks Braids, Arisen Nightmare 3.4%inclusion 106 decks 3.15K decks K'rrik, Son of Yawgmoth 2.8%inclusion 89 decks 3.15K decks Zul Ashur, Lich Lord 3.1%inclusion 88 decks 2.83K decks Iname, Death Aspect 2.7%inclusion 86 decks 3.15K decks The Ghoul, Gunslinger 3.3%inclusion 64 decks 1.94K decks Ashnod, Flesh Mechanist 2.0%inclusion 63 decks 3.15K decks Moseo, Vein's New Dean 4.1%inclusion 56 decks 1.37K decks Shirei, Shizo's Caretaker 1.7%inclusion 54 decks 3.15K decks Ghoulcaller Gisa 1.7%inclusion 53 decks 3.15K decks Ayara, First of Locthwain 1.6%inclusion 51 decks 3.15K decks Trazyn the Infinite 1.6%inclusion 50 decks 3.15K decks Ardyn, the Usurper 1.9%inclusion 44 decks 2.35K decks Gisa, the Hellraiser 1.3%inclusion 42 decks 3.15K decks Balthor the Defiled 1.0%inclusion 32 decks 3.15K decks Tergrid, God of Fright 1.0%inclusion 30 decks 3.15K decks Yawgmoth, Thran Physician 1.0%inclusion 30 decks 3.15K decks Tinybones, Bauble Burglar 1.0%inclusion 29 decks 2.83K decks Sheoldred, Whispering One 0.9%inclusion 28 decks 3.15K decks Sheoldred 0.9%inclusion 28 decks 3.15K decks New Cards Doombot Harbinger 4.1%inclusion 2%synergy 31 decks 753 decks Ultron, Artificial Malevolence 3.6%inclusion 0%synergy 29 decks 811 decks Too Evil to Stay Dead 3.2%inclusion 1%synergy 24 decks 753 decks Robot Domination 3.0%inclusion 1%synergy 24 decks 801 decks M.O.D.O.K

Making 2/2 fliers when you don't have a suitable army to pump is good too and just being a planeswalker still holds lots of value as well