Whispike Survivors - Sword of the Necromancer

During a run, you get to choose abilities when you level up. The whip is your starting ability if you're not using a custom Whispike you have grown. When you level up just select the green whip and get it to level 10 and this will unlock. You can also use the farming method I explain in Attack on Whispike (90G) to get a Whispike grown with abilities and levels from the start of a run which will make getting abilities to level 10 much easier. Once you hit level 10 with the whip the achievement will unlock.