Welcome to Is it Missed? #2 featuring yet another 2/3 for 3. I swear it's a coincidence. Oakheart Dryads has a constellation trigger that reads:
"Whenever Oakheart Dryads or another enchantment enters the battlefield under your control, target creature gets +1/+1 until end of turn."
The basic scenario is that you cast an enchantment pre-combat with an Oakheart on the battlefield, say nothing, then attack with the Dryads.
Is it missed?
Yes, it is missed. This might be surprising to you if you tuned in last time because on the surface, it seems the same as Kragma Butcher. They are both creature pumps. The difference is in the details, and the important detail here is that Oakheart Dryads has a targeted trigger, and you must select a target at the appropriate time. Straight from the IPG:
"A triggered ability that requires its controller to choose targets (other than 'target opponent'), modes, or other choices made when the ability is put onto the stack: The controller must announce those choices before they next pass priority."
That means you must declare you target before passing priority after the enchantment resolves, which is before creatures enter combat. If you don't select your target and move into combat, you're out of luck. The same applies to any other targeted constellation triggers like Dreadbringer Lampads, Forgeborn Oreads, Goldenhide Ox, Harvestguide Alseids, Strength from the Fallen, or Whitewater Naiads.
(Is it Missed? scenarios are all assumed to be at Competitive REL and thus are subject to the rules of the IPG, Infraction Procedure Guide.