Digger is a brown ball that deal damage at the impact and dig a hole by striking 5 time on the same spot (including the impact one).
Damage : 12 per hit, 5 times (60 max without critical).
This upgrade is very similar to Digger, but striking 4 times instead of 5, but digging a bigger hole.
Damage : 18 per hit, 4 times (72 max without critical).
This upgrade shot 12 small Digger, striking 4 times each but not in a single spot like Digger or Mega-Digger. Instead, those 12 shot wander around the map, striking tank randomly.
Damage : 6 per hit, 4 times for each 12 shots.
Upsides and Downsides
Digger and Mega-Digger are very useful, since putting in a hole someone who can't get out of it can put him in difficulty.
Excavation is more powerful when used on a zone with many enemies, even if some shot can wander back at you.