Final answer:
At Tier 1, Weakspot makes your units' attacks ignore 20 armor. As of the 1/5/22 update, Weakspot and Sunfire Board can now be used at the same time, which was not possible before.
Step-by-step explanation:
The effect of Weakspot : Tier 1 is that your units' attacks ignore 20 armor. In the 1/5/22 update, an important change was made to Weakspot and Sunfire Board: they are no longer mutually exclusive. This means that you can now use both these effects simultaneously, potentially increasing the effectiveness of your units in battle.