You are a data scientist for a free-to-play mobile game. The product team wants to introduce **video ads** (e.g., rewarded videos and/or interstitial video ads). Design an evaluation plan to determine whether adding video ads is a good idea. Your answer should cover: 1) **Success metrics** and **guardrail metrics** (include tradeoffs: short-term revenue vs. retention/LTV vs. engagement). 2) How you would design an **experiment** (unit of randomization, eligibility, ad frequency/capping, ramp-up, stratification). 3) How you would estimate **incremental impact** on revenue and user experience (e.g., ad revenue offset by changes in IAP purchases, session length, churn). 4) Key threats to validity (novelty effects, selection bias if ads are opt-in, interference/network effects, bots/ad fraud) and how you would mitigate them. 5) How you would decide ship / don’t ship, including how you’d think about **power/MDE** and long-term effects.