I can't be bothered to actually mess with Twitter to check if this works, but I think RAW supports it.
The Investiture line of spells from Elemental Evil are not the most popular spells, but combining them with Find Steed has interesting possibilities. A controlled mount has 3 action options: Dash, Disengage or Dodge. Find Steed allows spells with a range of Self (wth no aura range attached) to also affect the steed. In a case of specific beating general, the Investiture spell would add a possible action to the steed and provide a conditional survivability buff. The actions granted by the Investiture spells do not fall under a specific category of action, so they may not necessarily be restricted for falling under a category of action a controlled mount does not normally have access to.
Paladin 5 with druid/sorcerer/warlock/wizard 11 could do this at level 16. A bard could do this at level 14. It's not the strongest combo, but the action economy could be fun.