One of Brawl's limitations was that the mana bases were inherently weak
Dex 22 Cards Most Expensive Keldeo EX 70,55 Keldeo ex 61,93 Keldeo 21,69 Distribution by Rarity
Under the current rules (as of writing this blog post) both of them would simply die as a state-based action due to the planeswalker uniqueness rule, so nothing special happens

This bingo card has a free space and 41 words: Catch a Shiny Pokemon, Do a Raid, Catch a Normal Type, Hatch an egg, Catch a new pokemon for your Dex., Battle a Team Go Rocket member, Catch a Grass Type, Look at the news, Accept a gift from a friend, Evolve a pokemon, Activate an incense/lure, Battle a real-life player, Complete a field research task, Catch a Water Type, Expand your storage, Catch a Fire Type, Get a new medal, Complete a special research task, Use a rare candy, Send a friend a sticker, Get something from the shop, Add a friend, Catch a Electric Type, Take a picture, Use a berry, Catch a Rock Type, Catch a Ground Type, Catch a Steel Type, Catch a Fighting Type, Catch a Flying Type, Catch a Psychic Type, Catch a Fairy Type, Catch a Poison Type, Catch a Dark Type, Catch a Ghost Type, Catch a Ice Type, Catch a Bug Type, Catch a Dragon Type, Spin a PokeStop, Feed a pokemon a berry and Train against a leader

youll spend more money in the long run opening packs/boxes attempting to pull it yourself
There is an obvious theme of utilizing cards from the new set that have the Undergrowth mechanic to build a sweet creature deck