What is the safest way to attain Razor's Edge achievement?

Question

This achievement requires completing The Gravedigger with 18 or more charges but what strategy would be best to do this the safest way? Is there a way to try this with as little risk as possible?

Answer 1

When the boss's health dips into the second red, try stacking the points. It's the safest way to get the achievement, but be careful!