In some of the weaker recent sets this would have been a rare
Drain synergies on Bastion of Remembrance, pingers like Thermo-Alchemist, and consistent noncombat damage from a card like Chandra, Awakened Inferno, spell doom for players that can't engage in combat
Conversely, your opponents can barely use their planeswalkers or infect creatures at all
If the target of Killer is illegal as the spell tries to resolve, it won't deal damage to any creatures
Depending on the art you could always run another Omnath if you like, although you could end up in pedantic T-pose arguments given that Omnath has four arms and tends to do more of an X-pose
In terms of the cards cheapest variants, Strength Bobblehead appears to be spiking the most