Grenchlers can only be damaged from behind. Despite the indication that this area is vulnerable to explosive blasts, it can be targeted and damaged by any weapon. Super Missiles appear to be the most effective, however. Strafing to reach the backside or attacking from a distance before it has targeted Samus are ideal strategies for neutralizing them.
Grenchlers can be observed swimming as well as walking and running. They are arguably more dangerous while in the water, especially when Samus does not yet possess the Gravity Boost and thus has limited mobility. It is also more difficult to target them efficiently due to the limited space there is to move about in the aquatic environments. However, they cannot use their secondary long-rage attack while swimming. They can leap considerably long distances, and can maneuver to higher and lower platforms. However, they still appear to have limits as to where they can reach.