The first new Cup that players will be able to participate in is the Element Cup. It was already outlined in the June update blog for Pokemon GO, and it's slated to begin on June 28 at 1 pm PDT. The Element Cup will come to a close on July 12 at 1 pm PDT.
New rules are the most exciting parts of a featured Cup in the Pokemon GO Battle League, and the Element Cup has an interesting outline. First and foremost, only Fire, Water, and Grass-type Pokemon will be allowed in the Element Cup. Though, dual-types are allowed as long as they have one of the base three.
Then there are further restrictions, one of which states that every Pokemon must have an evolution, but are only in the first form of their evolutionary line. On top of that, the Pokemon cannot exceed 500 CP.
Options for the Element Cup in the Pokemon GO Battle League
Based on the restrictions given for the Pokemon GO Element Cup, the picks that players have will be very limited. Good choices below 500 CP alone will be hard to come by.
One of the most dominant picks will likely be Cottonee. The Grass and Fairy-type Pokemon dominated a similar Cup in the past. It's very likely that the same meta plays out to a degree.
Ducklett, Bulbasaur, and Vulpix are also all highly rated Pokemon for the Element Cup precursors. Players have a couple more days to prepare before the Cup itself releases.