In my first month of playing Splinterlands, I've seen many decks that are unbelievably overpowered and unbeatable to bronze league.
The first deck that I found OP is the Mylor-Kron combo.
Kron the Undying - Since bronze only enables level 1 legendaries, Kron having heal and decent magic damage is enough to withstand opportunity monsters and deal damage to dodge monsters and having shields.
Mylor Crowling - Having this summoner counters monsters with melee damage, especially Death and Fire monsters. If comboed with Kron, it will become unstoppable to defeat since having a 3 magic damage is enough to kill most of the monsters and Mylor's thorn to kill backline monsters with opportunity or snipe abilities.
Additional monster to add: Unicorn Mustang
Having this monster will be able to tank the magic damage since Water splinter, which specializes to magic in Bronze league, since it has the Void ability.
Lastly, this deck is pricy since the Kron ranges for about 200 dec per day when rented, while Mylor averages for atleast 30 dec per day (if Im not mistaken), so if you only care about raising rating and not increasing your earnings, you might check and try this deck!)
(I am only a beginner to Splinterlands but I hope this post will help other beginners to improve to the game, like me.)