Murky vs Diablo
Diablo is very tricky to fight any mistakes and you are dead. To defeat Diablo before Fish Tank you need to slime him back and repeat 10-20 times.
What makes things tricky is you have to stay out of range of his overpower and dodge his fire blaze attack. His fire blaze always spread in the same direction no matter which way Diablo is facing. So you never want to be directly to the north, south, east, west of Diablo. You need to be standing off to a diagonal to not get hit.
If there are minions present kill his minions so that your minions will attack him which will help a lot.
If there are any walls you can kill do so. This prevents Diablo from stunning you into them and it is also a source of vision for the other team.
One you have fish tank you will be able to go toe to toe with Diablo.