The Hammer Brothers are a species of elite Koopa fighters that stand upright and throw hammers at passers-by. They were first seen in Super Mario Bros and have bigger shells than normal Koopas. They can also use special hammers to shrink their enemies. 
The Personal Terminal or PET, (pronounced "pet" in the original Japanese version of the anime and "P-E-T" in the English version) is an electronic device that plays an important role in the MegaMan Battle Network series of video games anime and manga (the latter two of which are known as MegaMan NT Warrior in the U.S.). The PET was invented by Dr. Tadashi Hikari, grandfather of series protagonist Lan Hikari-Megamanwiki
The Personal Terminal (aka PET) is an electronic device used in the Mega Man Battle Network video game series, it's basically Mega Man's version of the PDA - personal digital assistant.