What zombie in the original game digs underground to bypass plants?

The zombie that digs underground to bypass plants is Digger Zombie.

Digger Zombie’s defining tactic is burrowing beneath the lawn instead of walking normally toward the house. It travels underground from the right side, bypasses plants in its lane, then emerges near the left side and begins moving toward the player’s defenses from behind. That makes it a serious threat to vulnerable resource plants and back-line attackers.

The zombie is not simply a faster version of a basic zombie. Its underground movement changes the normal rules of lane defense: front-line Wall-nuts and attacking plants may be left untouched while the Digger Zombie approaches the house. Players can counter it with tools such as Split Pea, whose backward fire is designed for threats that get past the main defensive line.

Ladder Zombie, Snorkel Zombie, and Pole Vaulting Zombie also bypass defenses in different ways, which makes them common mix-ups. Ladder Zombie climbs over barriers, Snorkel Zombie uses water lanes, and Pole Vaulting Zombie vaults over one obstacle. Only Digger Zombie uses underground burrowing as its signature method.