Easier spiders
As outlined on the trivia page, the right-most spider will adapt to a player having difficulty getting past the spider room. To extend this behaviour to the other two spiders, the jump at 37733 should be removed:
POKE 37734,0
As the value at 34223 controls this behaviour, it too can be manipulated. The higher the value in this location is, the longer the pause between subsequent attacks by a spider (normally only the right-most spider, unless the above POKE is also used):
POKE 34223,x (where larger x results in a longer pause between attacks)
Higher jumps
The routine at 55421 handles the increase in velocity for a character's jump. It is capped at 7 by the instruction at 55426. This can be increased to 15, allowing significantly higher jumps for both Drutt and Berk:
POKE 55427,15
Changing the cap to 15 is sufficient to allow Berk and Drutt to jump approximately 5 screens' worth of vertical distance. This allows them to jump as high as level 1's entry door room (two screens above the Trap Door room) from the room at the bottom of the Trap Door shaft.
Quicker recovery after fall
When Berk falls, the check at 48958 determines whether Berk can recover instantly, or whether he is to be stunned. The conditional jump at 48962 will make Berk enter the stunned state if bit 3 of his velocity factor is set. This conditional jump can be removed, resulting in Berk being able to fall any distance and recover instantly:
POKE 48963,0
Infinite flying duration
The call at 48487 decreases Berk's remaining flying duration. This call can be bypassed:
POKE 48488,3
Disable hatch (level 3)
The hatch on level 3 can be disabled:
POKE 39151,201