the thing is, i would say on about 90-something percent of turns after turn 4 maybe, you will play at least one action, so fairy is just, a realllly good card. the same for druid- three actions isn't really that much, unless there are definitely no non-terminal actions, in which case druid is just not a card in the kingdom. there is more material to be had, probably, out of rewarding an ability to play actions cards, beyond peddler, but i would say that it's more fun when there's arbitrarity in that reward; druid rewards that one turn where you played three actions and got $5 by improving your current and future turns' ability to play three actions and get $5. peddler rewards playing 4 actions and having buys by giving you non-terminal money, what? those aren't related, and thus the decision is weird and different and instead of saying, engines become a lot stronger and easy to set up around turn 5, it says that at some point engines will be able to create more money and also a weird thing with remodels.
goblin is straight-up unavailable on the ~30% of boards that don't have copper trashing, which is yikes. other than that, thief that never misses is ok. your opponent has to re-evaluate whether they are gonna go for money in action cards or in treasure cards or some mysterious other thing. also i will get really angry when you trash my horns of plenty
unicorn, suffers from the sort of big problem of cards that want you to play/not play other cards, being that, you'll just look at the kingdom and say, are the trashing/attack cards better than unicorn (also that same sort of problem as goblin, about 20% of boards will just not have worthwhile trashing/attacks). that said, that isn't necessarily an easy or exclusive question, sometimes it messes with the order in which you build the engine. steward likes it a lot.
i think my favorite of these, thus, is dragon, sort of, i'm a fan of synergizing with the cards that are always out, and this one occasionally will just accidentally turn your council room-bm thing into an engine on turn 7, when you realize there's still time to get villages. really good attack, starts to get devastating when the green cards will occasionally force you to trash a wharf or something and thus engines can hit later, which is sort necessary from its buy condition.
not bad, overall.