ok

takes a few times but basically strategy is

they will stop at every ballista to destroy it

firstly use the gaps so when the first epic comes he will stop by it
before he comes try and get a blade just before the gap
drop oil and bomb together as quick as you can and put new ballista down 2 places from the blade

this should kill the first epic

realise normal wizards stop 2 places from a blade when in blades they die quickly

build blades and protect with ballista 2 places in front

next epic comes on the bottom
get ballista in last gap once he destroys them all
drop oil by gap and bomb and ballista
try also for blade if poss

the epics can get to the treasure but try and keep the right side with a ballista at the end to kill the epics

build as many blades and protect them
epics need oil and bombs to damage plus boulders if available

2 epics at the end attack them as hard as you can

once they have treasure out of the keep just stop and restart level as you have lost

try and figure out the order the epics come in and prepare to attack them to the right side of the dungeon

once I have killed the first epic I move to the right side and get blades in position with protection
sometimes it is better to let the epic get to the treasure before putting the ballista down to make sure the treasure does not leave the end zone a timely bomb can also help take them out

once you have the pattern protected blades in place the wizards are easily killed but keep an eye on the epics slow them down in the bladed areas for maximum damage and bomb them

boom it is hard I still play it and only manage to win 1 in 3