Silumgars Scorn is probably the best place to start
It even beats out Flawless Maneuver, which is free if you control your commander
They don't go away as steps, phases, and turns end, and effects that add mana "of any type" can't give you energy counters
On top of that, I think Mono-Blue Aggro is actually pretty good against the current iterations of Esper Control, unlike in Ravnica Allegiance Standard where the matchup was a lot tougher and I valued having access to a planeswalker out of the sideboard, so Im not too invested in the idea of a dedicated sideboard card for that matchup anyway
Douglas 1993-1999 Wizards of the Coast, Inc
It didn't make the cut in Strixhaven , and it won't anywhere else