Clockwork Beast

Clockwork Beast enters with seven +1/+0 counters on it.
At end of combat, if Clockwork Beast attacked or blocked this combat, remove a +1/+0 counter from it.
{X}, {T}: Put up to X +1/+0 counters on Clockwork Beast. This ability can't cause the total number of +1/+0 counters on Clockwork Beast to be greater than seven. Activate only during your upkeep.

30th Anniversary Edition

Masters Edition

Clockwork Beast comes into play with seven +1/+0 counters on it.
At end of combat, if Clockwork Beast attacked or blocked this turn, remove a +1/+0 counter from it.
{X}, {T}: Put up to X +1/+0 counters on Clockwork Beast. This ability can't cause the total number of +1/+0 counters on Clockwork Beast to be greater than seven. Play this ability only during your upkeep.

Beatdown Box Set

Clockwork Beast comes into play with seven +1/+0 counters on it.
Clockwork Beast can't have more than seven +1/+0 counters on it.
At end of combat, if Clockwork Beast attacked or blocked this turn, remove a +1/+0 counter from it.
o
X, oc
T: Put X +1/+0 counters on Clockwork Beast. Play this ability only during your upkeep.

Fifth Edition

When Clockwork Beast comes into play, put seven +1/+0 counters on it. At the end of any combat in which Clockwork Beast attacked or blocked, remove one of these counters.
o
X, oc
T: Put X +1/+0 counters on Clockwork Beast. You may have no more than seven of of these counters on Clockwork Beast. Use this ability only during your upkeep.

Can attack or block even if it has no counters.

Loses a counter even if it is affected by a Fog-like effect which prevents it from dealing damage.

Clockwork Beast’s last ability resolves, you can choose to put fewer than X +1/+0 counters on it.

If Clockwork Beast has seven or fewer +1/+0 counters on it when its last ability resolves, it can wind up a maximum of seven such counters on it. If it has seven or more +1/+0 counters on it, the ability will have no effect.

This is a change from the most recent wording. Now, if some other spell or ability causes +1/+0 counters to be put on Clockwork Beast, it can wind up with more than seven such counters on it.