Lightning, Lone Commando (Isshin, Two Heavens as One) One of the best Mardu Commanders around, Isshin definitely fits Lightning's vibe in terms of combat mechanics
This younger brother is the first card on our list to not cost 2 mana
He stared at me
Eventually he'll get bigger than you are, and you will die
It allows an artifact, sorcery, instant, or enchantment to have creature types like Eldrazi, giant, or elemental as part of its type line, which means that card can trigger abilities that trigger when you cast certain creature types or when certain creature types enter
However, both Philoctetes, No-Nonsense Instructor and Ling, Imperial Soldier are obvious core cards for any kind of Hero-focused Steel deck