Both final bosses are not hard at all. It's more of a reward for completing the final level.
That level itself was the real final boss.
We get to play as Fark who has a bit different moveset.
Understatement of the century, Spark.
After saving Spark from the virus Fark joins forces with him in order to defeat the true villain.
Of course they fuse.
As i said, beating the final boss is not a challenge after completing that hellish course.
Spark is so depressed after realising his actions were responsible for killing the entire world he is now contemplating suicide.
Fark becomes so mad after hearing that bullshit he turns into a real
boy formie. These guys are called formies btw.
He is having none of that.
That was a bit gay, Fark.
And so this is the ending.