Magic: The Gathering: What happens to an artifact's abilities once it is turned into a creature by Tezzeret, Agent of Bolas?

The artifact will keep its abilities, but because it's now a creature you may or may not be able to use them immediately.  Any creatures on the field are subject to "summoning sickness"... specifically, they can't use activated abilities with "{T}" (the tapping symbol) in their cost until you've controlled them for a turn. So if you just cast the Tumble Magnet this turn, you can't activate it (or attack with it) until your next turn... just as if you'd cast, say, Gideon's Lawkeeper. Abilities which don't have "{T}" as a cost usually can be activated right away... but as Steve mentioned, there's a rule which specifically prevents creatures from being equipped to something else, so the Equip ability won't work. Other than that though, abilities work just fine.  For example, if you animate a Traveler's Amulet, you can still sacrifice it to search for a land. PS: One complicated but slightly common interaction with Tezzeret is Inkmoth Nexus.  If you animate an Inkmoth, then turn it into a 5/5... it will keep its Flying and Infect abilities: you'll have a potent 5/5 flying infector.  At the end of the turn though, it will lose flying and infect as normal, but remain a 5/5 creature.  If you then activate the land's ability again in a later turn, it will gain flying and infect again... but return to being 1/1: whichever power-and-toughness-setting ability resolved last trumps the earlier one.  If you want to get back to being a 5/5 infector, you'll need to first activate the land, then use Tezzeret's ability again.

It keeps its ability. Just think of it as an "Ensoul Artifact"