Brotato

I've just confirmed a way to make this much easier than counting on luck to acquire store items totaling +50% Speed. While both Explorer and Soldier give a +10% Speed bonus, the best character to use for this achievement is Golem.

Golem comes with a Speed bonus of +30% when his health is below 50%. Despite being a temporary boost, the bonus does actually change the Speed % entry on the character stats table. Because of this, you just need to get boosts totaling +20% and then get your health below 50%, at which point the achievement will pop. I did this just now, reaching +21% in Speed boosts, and as soon as my health dropped below the halfway mark, the popup displayed in the bottom-left corner.

It does help to enable the Manual Aiming option when trying to drop your level, as this allows you to direct your attacks away from the enemies that are helping to drop your HP.

I thought this one was going to be a nightmare at first, but Golem made it simple, and I got the achievement relatively easily. Good luck, and have fun!

I got this this achievement very simply by doing the following turn Enemy health, damage and speed to 25% choose your character one with a higher speed obviously better but I choose Ranger who actually starts at 0 speed. At the end of each wave you get the level up option, now as the enemies are quite simple you shouldn’t need to overly worry about weapons and health, so on the level up option you want an increase in speed if no speed showing re roll until you get a speed option then buy it, then if any item on the weapon upgrade offers speed purchase that also. Be careful not to purchase anything that can damage health and make sure your not confusing attack speed with speed you want just the speed. I got to 52 speed by the 11th wave and then went on to improve weapons and completed the run for the achievement. Or you can just quit out once you get the speed achievement.