Age of Wonders: Planetfall (PC) - Achievement - No one could survive that!
Kill 5 units with a single tactical operation
First of all, it should be noted that this achievement can be done by killing your own units in tactical combat.
There are many later game tactical operations with AoE damage - I use the 'Shredder Bomb' in this video used by The Assembly. You may find the opportunity to come across this naturally, but if you haven't and want the achievement, the Reverse Engineer produced by The Assembly should be able to help you. They can use the 'Create Construct' ability to make a weak unit next to them, so all you need is 5 Reverse Engineers to create 5 constructs, make sure they are within close range of each other and then drop 2 Shredder Bombs on them, making sure at least the same 5 Constructs are within the blast radius both times, thus simultaneously killing them and unlocking the achievement.
It should be noted that tactical operations that do not do instant damage do not trigger this achievement (eg. PyrX Bomb in the Promethean tech tree which causes damage by choking the turn after it is used)