Gillman, their electric attack has like 200 tile range (or similarly crazy range) and does around 100 damage on hit, why this enemy with such a long range damaging attack is present in one of the starting cults is beyond me.
Grenade launchers in the hands of agents with good stats are significantly more accurate, actually. Not as deadly, of course.
The aimed range is pretty much the default, and around 50% chance to hit with one aimed shot per turn. Nothing particularly noteworthy except for the arcing and the damage. The latter is a bit much, I agree, especially since electric resistance isn't particularly easy to come by. Arcing weapons with extreme range are a nasty surprise, too.
OTOH, Gillmen are alien terror/bioweapons leased out to the cultists. It'd be a bit strange if they
weren't scary dangerous.