Cumulative

upkeep

At

the

beginning

of

your

upkeep,

put

a

rust

counter

on

each

artifact

target

opponent

controls.

Then

destroy

each

artifact

with

mana

value

less

than

or

equal

to

the

number

of

rust

counters

on

it.

Artifacts

destroyed

this

way

can't

be

regenerated.

When

this

enchantment

leaves

the

battlefield,

remove

all

rust

counters

from

all

permanents.