After completing Classic Mode, Story Mode, completed the hard badge, bought everything from the shop in Classic and Story Mode, Achieved all of the medals, playing Arcade Mode until I had enough bonus points to buy everything from the Bonus Shop, I feel that I have somewhat achieved something.
Need help on the riddles? The locations are: the first one is at E-2 and the answer is 9. The second one is at J-7 and the answer is 27. The third one is at A-10 and the answer is 0. The last one is at E-14 and the answer is 70. + this if you find it helpful ^ ^
My strategy is pretty simple. Keep upgrading your tower till max then upgrade the combat, archer and mage until max. Then upgrade castle till max. Try not to upgade mana unless u have to. Then keep upgrading mana till 9999 and spam paladins and wizards (same slots for elven and orcs) works for me :)
In the later levels, trials, and extras, if u send ur hero out he/she almost dies straight away so the hero needs more health. I just keep my hero back and let my units do all the work.
Defeating the cave of trial 5: I used phantom armor, fire succubus, mermaid, centaur archer, dragon rider and black knight. For spells, I had comet shoot, rain of arrows, athena protection, healing wave, freeze trap and hercules strength. You must have freeze trap and athena protection or the invisible goblin will tear you apart. You can switch rain of arrows out for lightning bolt. BUT, do not use phoenix strike as it throws the invisible goblin in the air towards your castle. Overall the strategy is to get your hero out and attack the fodder. When all your units are at max production send them out and use the the freeze trap on the invisible goblin. Then use all the other spells. If all your units are killed by the goblin then just keep trying you will get it eventually :). Plus this or copy to keep alive!