This is a departure from Remastered sets in the past
Because Breena is so efficient at loading up on +1/+1 counters I've leaned into it with a strong counter subtheme: we use those counters to draw cards off Dusk Legion Duelist, ramp with Scholar of New Horizons, have board wipe insurance with Felisa, Fang of Silverquill, and turn our team into lethal angels with Sigarda's Summons
Ultron is good alongside any artifact that has enters or leaves triggers, but Solemn Simulacrum is the gold standard when it comes to that kind of card
Generally speaking, there should always be more cost 1 cards than cost 2 cards, more cost 2 cards than cost 3 cards, and so on and so forth
By default, when you use Richard's ability, you are limited to cards legal in the format you're playing