X-Men First Class is probably canon, although you might read others who disagree. But what everyone agrees on is that it’s excellent.
In this first issue, we’re taken through an early X-Men adventure through a letter from Bobby to his mother. The team takes on a plantlike creature in the Arctic.
They start fighting it but then Professor X helps them see that the entity does not have malicious intent. Rather, some scientists had drilled into its habitat.
The X-Men clear up the misunderstanding.