For example, say you activate the last ability of a Chimeric Mass with three charge counters on it. After it resolves, you cast Giant Growth targeting it. It’s now 6/6. Then Diminish (“Target creature becomes 1/1 until end of turn”) is cast targeting it. Once Diminish resolves, Chimeric Mass would be 4/4. Activating Chimeric Mass’s last ability a second time would make it 6/6 again until end of turn.