Trial 4: All titans. The best way to beat him is to build walls with the cursor over his right knee (the one on the left on screen). It will push him back a little every time. Trial 5: Black dragon, goblins/little hobbit, elf hunter, succubus, witch, and elder wizard (any ranged units will do, but these ones worked pretty well for me). Spam lvl2 meteor if you have it. Don't forget to plus both of these so everybody can see!
This has been fixed as part of the 1.9.1 patch, thanks!