The Chosen Ones

Hmm, for me I think I'm more of a dormant member due to a very busy life Will post interesting stuff whenever I can.

I'll try

Holgro Part 1
For every 10 hits received, a shield will be applied to the hero which absorbs all incoming damage. The shield lasts for either 5 hits or 10 seconds, then the counter resets.

Holgro Part 2
For every 15 hits dealt, the hero will start dealing double damage. This lasts for 5 hits or 10 seconds, then the counter resets.

Holgro Part 3
For every 5 spells cast, the hero will cast spells without the need for mana. This lasts for 3 spells or 10 seconds, then the counter resets.

Full Holgro
For every 10 hits received, a shield will be applied to the hero which absorbs all incoming damage. The shield lasts for either 5 hits or 10 seconds, then the counter resets.
For every 15 hits dealt, the hero will start dealing double damage. This lasts for 5 hits or 10 seconds, then the counter resets.
For every 5 spells cast, the hero will cast spells without the need for mana. This lasts for 3 spells or 10 seconds, then the counter resets.
If two buffs are active at the same time, the hero will generate an aura that deals damage periodically (every 0.5 second) for 20 seconds.
If all three buffs are active at the same time, the hero becomes invulnerable, deals double damage, and can freely cast spells without the need for mana for 20 seconds.

Extra: Maybe make the hero change colour according the which buffs are activated. The first three parts will turn the hero red, yellow and blue respectively. If the hero for example has both red and blue buffs, the hero turns orange. If the hero has all three buffs, the hero turns black.

robotworld: Your whole theory is just wrong  .
Firstly, it doesn't make sense to me, but that's a personal opinion and it's not the main problem
Secondly...Dragons? Are you crazy? Well, maybe it could work if you don't use the dragons...

Aero: well, i said pillars as a example, you could put some tree like monsters that can't move, like that "tree like " night elf tower sprite, or maybe some kind of "great wisps".... I think many things would work("pillars,obelisks and temple like" things too in my opinion), but portals are in my opinion already used a lot so you should try to avoid them if possible.

My bad. Yes you are right, my theory is indeed very wrong. I misread the post. Thought I saw epic boss

Here's my revised version

- How does the wisp come?
The boss will summon some forest critters or treants which attack you. Killing them will turn them into wisps. The wisps then move slowly towards the tree boss.

- What happens after X wisps is gathered?
The boss will have increased movement speed/attack for every wisp that reaches the boss. The effect stacks and lasts for 2-3 minutes per wisp.

- How to make this boss spell tactical?
Make it such that when two wisps are in close proximity, they come closer together and disappear in an explosion. So the player may wait for a few whelps to spawn before killing them at one go. Give some delay before the wisps explode so the player can set up protective measures.

- How does the wisp come?
Maybe have little whelps that fly around the boss at random intervals. The whelps can attack you. Once you kill a whelp, a wisp spawn and moves slowly towards the boss.

- What happens after X wisps is gathered?
A giant dragon appears in the boss place and attacks you for a while before disappearing. Boss appears again and the cycle continues

- How to make this boss spell tactical?
Make it such that when two wisps are in close proximity, they come closer together and disappear in an explosion. So the player may wait for a few whelps to spawn before killing them at one go. Give some delay before the wisps explode so the player can set up protective measures.

Here's one with Fradz. Whenever I turn invisible, and attack an enemy, if I click at another place for Fradz to move at the last minute, bonus damage is dealt but I stay invisible. Using this tactic I managed to clear Chp. 2 with a breeze.

Also, the Momo boss in Chp. 2 doesn't do anything after I turn invisible. It just stands there waving its stick about.