So in the description it states "... armed with impact explosives for underwater use and quadruple shotgun when on land". However, in the water it uses both the shotgun and the impact explosives and when it is tossed by a lobster in the water, it initially fires shotguns and then as it sinks it fires the impact explosives which gives a massive amount of damage for a 280m unit. About 400 DPS total - (261 shotgun + 128 explosive) against a combined underwater + surface fleet/aircraft.
The Claymore, a 300m unit, has 113 DPS and only 160 more HP than the Scallop - 1260 to 1100 so it is completely out-classed.
The Corsair, a 240m unit, has 117 DPS and only 250 hp more than the Scallop - 1350 to 1100 and it cannot shoot underwater so again it is completely out-classed. It is faster than the Scallop, but that is completely negated by a single Lobster. Plus the Corsair cannot defend itself at all against Scallops walking underwater.
Additionally the only air unit than can directly target underwater units is the Raven.
Here are 2 different options to balance Scallops:
1. Increase cost to about 500m plus Lobsters cost 500m.
2. When in the water/air Scallops should be unable to fire shotguns and Lobsters can stay the same cost.
In addition to 1 of the 2 options above, give 1 more aircraft unit the ability to target submerged units, 2 gunships the same, and all except the Mariner, Envoy and Zephyr ship units the same.