The second labor was to kill the Hydra Lernaia which haunted the swamps of Lerna. Herakles easily decapitated its heads, but two would come out of the same cut neck. He and his nephew, Ioloas, decided to cauterize the decapitated necks after they would cut off the head, it worked. A large crab tried to help the Hydra, but Herakles crushed it with his heel before ot could do any harm. Hera gave them a consteallation, the crab was cancer and the Hydra was.. Err... I'll look it up.
The third labor was to fetch the Elaphos Kerynitis, a sacred golden horned deer of Artemis. Herakles chased the deer for a full year, eventually he caught it on mount Artemision in Arkadia. Artemis complained about the condition of the deer, since Herakles broke its horn while trying to tame it. He told Artemis that he will only borrow the deer for the labor, she accepted the terms.
The fourth labor was to capture the Hus Erymanthios, it ravaged the farmlands of Psophis in western Arkadia. Herakles found the boar in the freezing mountain of Etmrymanthis, he then netted the beast and brought it back to king Eurystheus. Terrified, the king hid himself in a buried Pithos jar.