Crit and/or Tryndamere remake.
Apart they are flawed together they are broken and unfun. Crit is an entirely luck based mechanic, ive seen people with 20% crit manage 4 crits in a row due to being lucky Crit should be changed where the % refers to 1 in X and not rely on RNG.
Now I know Tryndamere is one of Riots golden boys and therefore immune to proper balancing but he is a joke. Make CC stop his ult, make him take a portion of the damage dealt during his ult after it ends, remove his innate crit. Or better yet give him a full rework. Thankfully you dont see many.