The main consideration is narrowness, since it only counters noncreature spells and the alternate cost does not work on your turn
In Gruul there's the potential for lots of mana-based payoffs to generate more combats and thus generate more and more and
A rarer card will have much less supply, and rare cards are often the ones in demand for Constructed decks since theyre also typically stronger
Kelpie Guide Kelpie Guide exists in a similar space to Ley Druid, but its far superior, both for its greater flexibility and because blue just gets this ability less often
Special features include: Saga Creatures - Summons are making an appearance in this set, as part of Magic: The Gathering's first-ever Saga creatures
Equipment decks usually have three or more artifacts on the battlefield, so its usually pretty easy to meet the requirement