Executioner vs Slayer

you want grievous wounds vs mundo

Or you can get + but thats gold wasting on another level lol

Mortal reminder is far stronger because it gives you roughly 24-30% (depending on having SV or not) of his max health as TRUE DAMAGE by reducing his healing from his ult.

Think about it this way, grievous wounds reduces incoming healing by 40%. This is the exact same functionality as if whenever a champion healed, they were dealt true damage equal to the grievous wounds percentage.

increases your physical damage by 15% which gets reduced by armour

reduces his ult healing by 15.84 / 20.16 / 24% of his max HP if applied for all 12 seconds, increased to 19.008 / 24.192 / 28.8% if he has - effectively doing that much %HP true damage