Undercover Frogs

Each turn during your end step Undercover Frogs take +1/+1 from target creature opponent controls and adds it to themselves. If target creature opponent controls goes to 0 strength
then that creature becomes a land with ability
{t} then gain {g}.
"When frogs appear around camp, beware. Gaea frequently uses them as spies."
- Lazarus Strife of Llanowar