Helmut Krabbe's name implies that it is a crab, but it looks more like a hermit crab (Hermit crabs aren't actual crabs!). Has a 100% chance to survive 1 lethal strike and it has a fast attack rate. As usual, meatshields are good here. It won't be much of a threat if stalling is fast.
Being the 3rd Alien enemy introduced, it is not much of a threat as long as you have anti-Alien Treasures. The only problem is the lethal strike resistant ability. To kill it, use meatshields and Valkyrie Cat. If you have Bahamut Cat, use him. Then use the Cat Cannon to finish it off.
Later on, Helmut Krabbe becomes very easy. It shouldn't be a problem at all. At best, it's free money; at worst, it'll serve as protection for more threatening enemies.
Took out a 45-year loan on a durable home to cover up the THAT growing from his rear. Still spends every weekend at open houses. Can survive one lethal strike.