Yep, it can get broken pretty fast
Auras, Equipment, and modified creatures you control gain hexproof until end of turn
3 Combat Celebrant One For All, All 4/1 Combat Celebrant was deliberately designed not to produce infinite combat loops, but it turns out you can just make copies of Celebrant and exert those instead to set up as many combat steps as you need
Ramp For Counter-related stuff, there's Devoted Druid, Incubation Druid, Rishkar, Peeme Renegade, and a bunch of other stuff
Forced Transformation: The Oracle spell Foxfire and Beowulf's sword skill "Chicken" can cause enemies to turn into Chickens if their Brave drops low enough
With that in mind, heres a look at the rarest and most expensive Magic: The Gathering cards, why collectors covet them and how much theyre selling for