Your opponent doesn't have to explicitly say "I activate..." to use a card's effect.
Here's why:
* Effects happen automatically: In Yu-Gi-Oh, many card effects are triggered by specific events, like summoning a monster or changing a battle position. These effects happen automatically. For example, if you summon a monster with a "when summoned" effect, that effect triggers without any announcement.
* No "Declare" phase: Unlike some other card games, Yu-Gi-Oh doesn't have a separate "Declare" phase where you announce the effects you want to use. Actions usually happen directly in the Main Phase or during other phases.
When you DO need to announce:
* Some effects require a specific declaration: For example, certain trap cards require you to announce their specific effect before activating them.
* If you want to be clear: While not mandatory, it's a good idea to announce when you're using a card's effect, especially for complex effects or if you're unsure about the rules. This helps prevent confusion and arguments.
Example with Balloon Lizard:
* If you want to use Balloon Lizard's effect to add counters: You don't need to say, "I activate Balloon Lizard's effect."
* Instead: You simply say, "I place a counter on Balloon Lizard." Or, "I place three counters on Balloon Lizard."
Key takeaway: It's important to understand the specific card effects you're dealing with. If the effect is triggered automatically by a specific event, no announcement is required. However, it's always a good practice to be clear and communicate with your opponent, especially for more complex situations.