Chimeric Egg

The clock runs on your opponent's terms, which is the genuinely strange part. Most charge-counter artifacts feed themselves on your turn or off your own actions; this one only ticks forward when an opponent casts a nonartifact spell, turning their development into fuel for a 6/6 trampler. The effect is a punish disguised as a creature: a control opponent slinging counterspells and removal builds the counters faster than they realize, while a deck that durdles politely can leave the Egg cold indefinitely. Three counters means three opposing spells before the body even threatens to activate, and the transformation expires at end of turn, so each animation is a one-shot. That detail stops it from being a permanent threat any deck quietly runs as a beater: you have to recharge across multiple turns of opposing activity to fire it again, which makes it a slow-rolling clock that rewards patience against an active caster rather than a reliable finisher. Among the artifacts that read the opponent's behavior instead of your own, this one sits at an awkward intersection: a colorless body that fits any shell, paired with a payoff that needs a specific kind of opponent to do anything at all. Against an artifact-heavy or spell-light opponent, it never wakes up; against one casting nonartifact spell after nonartifact spell, it becomes a quiet tax on every card they play.