Clockwork Avian
Artifact Creature — Bird
Flying
This creature enters with four +1/+0 counters on it.
At end of combat, if this creature attacked or blocked this combat, remove a +1/+0 counter from it.
, 
: Put up to X +1/+0 counters on this creature. This ability can't cause the total number of +1/+0 counters on this creature to be greater than four. Activate only during your upkeep.
Randy Asplund-Faith
Fourth Edition (4ED)
• #306Rulings
If the ability to add counters resolves when there are already the maximum number of counters on it, any counters over the maximum are simply not added.
(wotc • 2004-10-04)
Loses a counter even if it is affected by a Fog-like effect which prevents it from dealing damage.
(wotc • 2004-10-04)
Can attack or block even if it has no counters.
(wotc • 2004-10-04)
Rulings
If the ability to add counters resolves when there are already the maximum number of counters on it, any counters over the maximum are simply not added.
(wotc • 2004-10-04)
Loses a counter even if it is affected by a Fog-like effect which prevents it from dealing damage.
(wotc • 2004-10-04)
Can attack or block even if it has no counters.
(wotc • 2004-10-04)