From RWP Wiki
Mount Fire-Eyes is an unused fire themed level from Banjo-Kazooie. It has been assumed that Mount Fire-Eyes was used instead as a basis for the fire side of Hailfire Peaks in Banjo-Tooie. In Banjo-Kazooie, Gobi is last seen stating that he is going to "the lava world," and it is revealed in Banjo-Tooie that he was talking about Hailfire Peaks.
Another theory is that 'Eyes' was a play on "Mount Fire-Ice" and there could have been a twist with eyes as being a part of the fire-ice theme.