Revenge

Revenge
Challenge
Unlock criteria	Reach zone 80 in U2 for the first time
Reward	Perk: Hunger
Goal	Complete zone 80
Rules
Enemies have 10x health on even zones
When Trimps are killed, 7.5x of the overkill damage received will hit the next group of Trimps. Any group killed will cause 1 "Revenge" stack to be gained.
Every "Revenge" stack increases attack and health by 20% (additive). Reaching 20 stacks of Revenge will fail the challenge.

"Travel to an exceptionally harsh dimension filled with vengeful creatures, including the Trimps. Enemies have 10x health on even zone numbers. If your army is killed at any point, any overkill damage will be applied 750% to the next group of Trimps to fight. Any time a group of Trimps is killed by this Overkill damage, your Trimps gain a stack of 'Revenge', increasing their Attack and Health by 20% (additive). However if your Trimps ever reach 20 stacks of Revenge, you will instantly fail the Challenge. Clearing Zone 80 with less than 20 stacks of Revenge will complete this Challenge."

Revenge is a new challenge introduced together with the Radon Universe. This is the second challenge after Bublé that can be ended prematurely (without abandoning), and rewards the Overkill Perk for U2.

Rules

All enemies in even zones will have 10x health.

Every time Trimps die, 7.5x of overkill damage will be dealt to the next group of soldiers.

If this damage exceeds the amount of health of the next group of soldiers, they will spawn dead. This causes 1 stack of Revenge to be applied to your Trimps, increasing attack and health by 20%(additive).

Reaching 20 stacks of Revenge will cause the challenge to be failed instantly.

Strategy

If Trimps die due to the "Abandon Soldiers" button, the overkill damage is 0 and your next group spawns with full health. So suiciding is a viable strategy if you can time your key-presses properly, and avoids Revenge stacks from accumulating too quickly.

Invest in Prismatic Shield and Equality, and turn off Equality Scaling, once Revenge stacks are close to 20.

A risky strategy is to obtain 19 Revenge stacks early on (for the attack/health boost), then respeccing mid-run to Equality and other health/Prismatic Shield-boosting Perks, then avoid getting Overkilled for the remainder of the run. This will also gain the feat for the challenge if done successfully.

Trivia

Before patch 5.4, this challenge gave the Overkill perk as a reward.