Avalon: Routine at D71C

Executed after 8 game timer cycles. Combined with a pseudo-random number, this affects the likelihood interval of a creature (spider/bat) appearing in the tunnel.

The room number is one of the variables in this calculation
There's a slightly lower chance of creatures appearing in higher numbered tunnel rooms
The room tunnel numbers (6710) start high and decrease for deeper levels within the game - e.g. interconnecting tunnel room numbers within the Gatehouse Level are 251-255
This means Maroc will tend to encounter more creatures within Avalon's deeper tunnels

Used by the routine at D6D2.
Jump from D6E0 if no new tunnel wall has been generated during this particular game cycle. Every 8 game cycles, there's a chance of a creature appearing.
D71C	LD A,($EAAA)	Get the game timer
D71F	INC A	Increment it
D720	AND $07	Check bits 0-2 (values 0-7)
D722	JR NZ,$D794	Check bits 0-2 (values 0-7)
Executed after 8 game timer cycles. Combined with a pseudo-random number, this affects the likelihood interval of a creature (spider/bat) appearing in the tunnel. The room number is one of the variables in this calculation There's a slightly lower chance of creatures appearing in higher numbered tunnel rooms The room tunnel numbers (6710) start high and decrease for deeper levels within the game - e.g. interconnecting tunnel room numbers within the Gatehouse Level are 251-255 This means Maroc will tend to encounter more creatures within Avalon's deeper tunnels
D724	CALL $DB06	Generate pseudo-random number in A register
D727	LD C,A	Store in C register
D728	LD A,($EAB7)	Get room number
D72B	SUB $30	Because tunnels are rooms 224-255, this will result in a value somewhere in the 176-207 range
D72D	CP C	Is this value greater than the random number?
D72E	JR NC,$D794	If so, jump out of here If not, continue to the next routine to generate a SPIDER or a BAT