I, Enguarde, have put how to beat each boss in DKC below:
In order...
1. Very Gnawty - Jump on his head
five times. While he is standing still right after being hit, he
is temporarily
invulnerable. Wait until he starts jumping around again.
2. Necky's Nuts - Jump on his head
five times. Before he spits the coconut, he is invincible.
You must
get him between when he spits the nut and when his head leaves the screen.
3. Bumble B. Rumble - Hit the bee
with a barrel five times. While the bee is red (right after
being hit)
it is temporarily invincible. Just avoid it then.
4. Really Gnawty Rampage - Jump on his head five times.
5. Boss Dumb Drum - Avoid the drum
(which will try to squash you) and then kill the
monsters
that it dumps. Repeat for five sets of monsters.
6. Necky's Revenge - Jump on his
head five times. This one is just like "Necky's Nuts," except
it spits
more nuts after each hit (one the first time, two the second time, etc.).
7. K. Rool - you have to dodge several
things in various stages (K. Rool's thrown crown, by
jumping
over it; cannonballs, by running between them; K. Rool himself running,
by jumping
over him;
and K. Rool jumping, by moving under him). Jump on K. Rool's head when
his
crown is
off. It takes nine hits to finish him off.