What would happen if you target a animated land with Mirrorweave?
Yes, the other creatures will be Mutavault lands until end of turn, but they will not be 2/2 creatures. You can, however, animate each of those lands through their copied animation ability.
A copy effect only copies what's printed on the original card and other copy effects, but no other effects. The animation effect from Mutavault is such an &quot;other effect&quot; that will not be copied. The example given in the rule covers pretty much exactly your situation.

706.2. When copying an object, the copy acquires the copiable values of the original object’s characteristics and, for an object on the stack, choices made when casting or activating it (mode, targets, the value of X, whether it was kicked, how it will affect multiple targets, and so on). The “copiable values” are the values derived from the text printed on the object (that text being name, mana cost, color indicator, card type, subtype, supertype, rules text, power, toughness, and/or loyalty), as modified by other copy effects, by its face-down status, and by “as . . . enters the battlefield” and “as . . . is turned face up” abilities that set power and toughness (and may also set additional characteristics). Other effects (including type-changing and text-changing effects), status, and counters are not copied.
Example: Chimeric Staff is an artifact that reads “{X}: Chimeric Staff becomes an X/X artifact creature until end of turn.” Clone is a creature that reads, “You may have Clone enter the battlefield as a copy of any creature on the battlefield.” After a Staff has become a 5/5 artifact creature, a Clone enters the battlefield as a copy of it. The Clone is an artifact, not a 5/5 artifact creature. (The copy has the Staff’s ability, however, and will become a creature if that ability is activated.)