Does vision stack if I have two Forecaster in the base?

Yes, Vision stacks if you have multiple Forecasters in play.

According to RiftJudge FAQ #84:

"Multiple Forecasters do stack, so playing a mech with multiple Forecasters in play will trigger vision multiple times."

How it works:

• Separate Triggers: Each instance of Vision triggers independently when a Mech enters play.
• Resolution: When each trigger resolves, you look at the top card of your Main Deck and choose whether or not to recycle it.
• Sequence:
  1. A Mech enters play.
  2. The first Vision trigger activates (you look at the top card and choose to recycle or not).
  3. The second Vision trigger activates (you look at the top card again and choose to recycle or not).

Nuance: If you choose not to recycle the card during the first trigger, the second trigger will see the same card. This allows you to look at the same card multiple times or, if you choose to recycle, to cycle through multiple cards in your library in a single sequence.