In the context of the problem, the event we are interested in is the first draw being a green token.
Initially, there are a total of:
- 10 blue tokens,
- 8 green tokens,
- 12 red tokens.
Calculating the total number of tokens, we have: \[ 10 + 8 + 12 = 30 \text{ tokens in total}. \]
When Marcus draws the first token, for this specific event (drawing a green token), we must consider only the green tokens. There are 8 green tokens available.
Since we are asked for the number of favorable outcomes for the event that the first draw is a green token, the answer is simply the number of green tokens available to draw.
Thus, the number of favorable outcomes for this event is: \[ \boxed{8}. \]