Pro tips: get the permanent items at the goblin shop as fast as you can, once you get the hero to lvl 5 get the chaos mine magic and spam it near the point you want to defend before starting the first wave on each level, upgraded elven archers are very good against single targets, one doomhammer + 2 ninjas is a very good combo, against invisible targets you can teleport your hero close to them so your defences can engage them when they reappear, you can repeat a level to get extra exp for your hero or extra gold.
Tips for rush mode/any lvl on epic: use mage hat/mage robe/mana staff. Now for the spells: freeze, bolt and heal (max them out if possible). Combat: you can take groups of mobs by using bolt on all of them. Heal will normally restore you up to full health with just one try. To regen mp simply kite an easy mob or freeze a mob/s and hit it repeatedly. With this trick there is no need to look for hearts/mp orbs.
For bosses: Temper and heal are all the you need. Gear with all the +att you can -unless u have ninja gear/umbrella which give maximum mobility-. Memorize the attack patterns and look out for gaps in their attacks.
Time trial medals: ninja gear/umbrella. Bounce/evade enemies when possible.
Sharing set-up for alien campaign completion: Ability/Static field, weapons: choose rocket launcher when possible, equipment/adrenaline boost/power extender (makes those power ups last 40% more)/hair trigger (faster rate of fire=more kills).
Tactics: always try to get the powerups (invincibility powerup as priority), try to make the guys follow you (kite), shoot off screen (sniper rifles can do so), use the field as close to the enemy as you can, always aim to have a shields, use weapons that don't require direct aim (ice hunter, particle cannon, hail storm, shredder).
Tip for final level and all those levels with rockets, use the shield ability it can one hit ko enemy if used properly (especially if enemy is using powerups for dmg/speed and rocket launchers).
One thing: game is great overall. Just could add some polish though, the hard campaign is frustratingly difficult due to one simple reason: friendly ai is just terrible, they keep getting killed (many times helping the enemy get a fast score. rocket race mission comes to mind), or simply not helping you out and dying fast as hell (last mission from hard difficulty). This makes the game feel unnecessarily cheap. e.g. last mission score me 14 kills 2 deaths, first ai guy 3 kills 8 deaths, second ai guy 1 kill 8 deaths.
Lol last building is broken, you spam it (+10% dmg per building), and guess what, killed the last boss in 3 hits(phoenix spam), and normal mobs were dying with one hit. Dmg was around 11 k, yep over 9 THOUSAND!!! lol
3370 dmg with one hit - Maxed demon lord + rage + artlogic's badge. Half health? Regen and less 15 seconds later back at full health (3x speed). Awesome.