conf t
access-list 10 deny 192.168.50.0 0.0.0.255
access-list 10 permit any
end

# VLAN 1 DEFAULT NATIVE
conf t
vlan 1
interface vlan 1
ip address 192.168.0.1 255.255.255.0
ip nat inside
ip access-group 10 out
end

# VLAN 20
conf t
vlan 20
name Dev
interface vlan 20
ip address 192.168.20.1 255.255.255.0
ip nat inside
ip access-group 10 out
end

$ ping 192.168.0.200
PING 192.168.0.200 (192.168.0.200) 56(84) bytes of data.
From 192.168.50.1 icmp_seq=1 Packet filtered
From 192.168.50.1 icmp_seq=2 Packet filtered
From 192.168.50.1 icmp_seq=3 Packet filtered

$ ping 192.168.0.1
PING 192.168.0.1 (192.168.0.1) 56(84) bytes of data.
64 bytes from 192.168.0.1: icmp_seq=1 ttl=255 time=17.9 ms
64 bytes from 192.168.0.1: icmp_seq=2 ttl=255 time=30.4 ms

$ ping 192.168.20.1
PING 192.168.20.1 (192.168.20.1) 56(84) bytes of data.
64 bytes from 192.168.20.1: icmp_seq=1 ttl=255 time=2.73 ms
64 bytes from 192.168.20.1: icmp_seq=2 ttl=255 time=23.7 ms