All Will Be One will deal damage coming and going, first pinging someone for every spell cast, then again when we move the counters off of Forgotten Ancient during our upkeep
While that ends up being close to negligible in the Underground Sea case where shipping will be $2-3 for a $250 card, it ends up being extremely relevant when dealing with $3-5 cards like Golgari Grave-Troll
Another solution is simply to play Destructive Flow in a deck full of cheap cards and kill your opponent with one- and two-drops while no one can cast anything bigger
However, they are only legal in Vintage in which they are restricted, meaning a deck may not contain more than one copy of the cards
I have quite a few cards without Flash, however, and I decided rather than cut them, to instead run Vedalken Orrery, Leyline of Anticipation and Teferi, Mage of Zhalfir