Poppy, Defender of the Meek

Keywords in this card's text

Ambush

Play the unit with Reaction timing at a battlefield where you control a unit—even if you do not control that battlefield. Normal costs and exhausted entry still apply unless card text changes them.

Reaction

Includes Action's timing and also lets you respond to a spell or ability before it resolves.

A Reaction can start a chain; it does not have to answer another card. It cannot interrupt an effect that is already resolving.

Tank

Assign lethal combat damage to that side's Tanks before its non-Tanks. The player assigning damage chooses the order among multiple Tanks. This does not protect other units from targeted spells.

How Focus and Priority decide when Action and Reaction can be used