8-10? Good.
Here's my first idea.
Steam Warrior
Maximum mana is set to 1000. It cannot be more or less. (with items that have Intelligence and mana increases, it is easier to keep maximum at 1000 than 100) He has no mana regeneration. Mana represent Steam for him. Any time he gains more than 66% Steam, he has a chance to explode. (Goblins are Goblins)
Full Throttle!
The Steam Warrior generates 15% Steam per seconds for 10 seconds.
Powerful regenerative ability, but it must be used with caution, because it can easily let the SW to explosion.
Reinforced Cauldron
Passive. Absorbs up to X damage from each enemy attack. Damage cannot be reduced below Y damage. Also slightly reduces explosion chance.
Pump the Steam!
Passive. Each hit has a X% chance to generate 15 Steam.
Coal to the Cauldron
Adding more coal to the steam cauldron, the Steam Warrior overheats, dealing X damage per second to all nearby enemies and generating 5 Steam per second for 12 seconds.
Release Steam
Releases all accumulated Steam, dealing X damage per point of Steam to all nearby units, both friend and foe. Long cooldown.
Emergensy ability, in case the SW has too much Steam and is close to exploding.
Boiling Steam
25% Steam.
Deals X damage to the target and forces the target attack the Steam Warrior.
Ranged.
Steam Punch
20% Steam.
Deals X bonus damage on attack.
Melee. Based off Searing Arrows.
Jigsaw
10% Steam per Second
Channeled. Deals X damage per second to the target. Also reduces target's armor by Y for 10 seconds if channeled for whole duration.
High-damage ability with rather long cooldown. I suppose you use Shredder model for SW, so the saw seems approppriate.
Earthquake
75% Steam
Deals X damage to all nearby enemies, slowing their movement speed by 50% and reducing their damage by 60% for Y seconds. Also forces them attack the Steam Warrior.
Combination of Thunder Clap, Howl of Terror and Taunt. Very powerful ability, but requires lots of Steam and as such is dangerous.
Pressure to Hull
35% Steam.
The Steam Warrior diverts part of steam pressure to hull, increasing his armor by 100% + X for Y seconds.
Steam Rocket of Doom
50% Steam.
Launches a powerful steam-powered rocket at the target, dealing X damage and stunning the target for 5 seconds. Very unreliable.
Deals high damage, but with 25% chance deals all that damage to Steam Warrior instead. Goblins are Goblins.
Clarification:
Steam explosion deals damage to the Steam Warrior equal to 50% of his maximum health, reduces mana to 0 and stuns him for 6 seconds.
Bombardier
Firebomb
Fires a bomb at the target, which deals X damage to the target and all units near it.
Frag-Bomb
Fires a bomb at the target, which deals X damage to the target and all units near it, stunning them for 2 seconds and reducing their armor by 50% for Y seconds.
Chem-Bomb
Fires a bomb at the target, which bathes the target and all units near it in sticky and highly acidic chemicals, dealing X damage per second and reducing their movement speed by 50% for Y seconds.
Shrapnel Squall
Deals X damage to all targets in front of the Bombardier, stunning them for 3 seconds.
Based off Shockwave/Carrio Swarm. Short-range, used mainly as self-defense.
Ready! Aim! BOOM!
Deals X damage to the target.
The only single-target ability of Bombardier. Has a 33% chance to hit a different target (random) near the original one instead (even ally!) so has to be used with caution.
Proximity Mine
Lays a proximity mine on the ground. It takes 3 second to arm and will explode when approached by any unit, dealing X damage to all units within range.
Remote Mine: Lay
Lays a remote mine on the ground. The mine persist for X seconds and deals Y damage when detonated.
Remote Mine: Detonate
Detonates all remote mines within X range. Y second cooldown.
Bombardment
Passive. Increases damage and area of effect of Bombardier's auto-attack.
Cannon Barrage
The Bombardier unleashes a barrage of gunfire at target area, dealing X damage per wave, for a total of Y waves. The shells also burst into flames, dealing Z damage per second for 3 seconds to any unit hit.
Basically a Rain of Fire with this model.
Grenade
Tosses a grenade at target area. After 2 second the grenade explodes, dealing X damage to all units near it.
Artillery Strike
The Bombardier call for an ordnance strike from his own experimental cannon, hidden somewhere... safe... Deals X damage to all targets within Y area. The area is centered on a random unit (preferably enemy one, but you cannot be sure, when it comes to Goblin technology) within 1000 range of the Bombardier.
I'd suggest some nuclear explosion model.
Mage
Spells cost a lot of mana, so the player must conserve it. KABOOM! and Sub-Zero cost no mana, but Sub-Zero is dangerous (and boring)
Conflagration
Deals X damage to all units in target area and additional Y damage to each unit hit over 6 seconds.
Incinerate
Deals X damage over 15 seconds to the target.
Combustion
Passive. All spells (Except Sub-Zero) have a X% chance to ignite the target, dealing Y additional damage over 6 seconds.
KABOOM!
Deals X damage to all enemy units afflicted with Combustion, Incinerate or Conflagration, consuming them in spectacular explosion.
Damages units near affected targets too. Costs no mana.
Flame Surge
Deals X damage to up to Y enemies in front of the Mage.
Based off Forked Lightning. Spirit Link lightning effect works perfeclty.
Lightning
Deals X damage to the target.
Based off Chain Lightning, hits one tareget only. Basic spell - not very powerful, not expensive.
Mad Spell
The Mage casts a crazed spell, which lingers in the air for 4 seconds and then explodes, dealing X damage to all units within formidable range.
Very high damage. Nuclear explosion effect.
Flame Gate
The Mage teleports to the target point, dealing X damage to nearby enemies on both point of his deprature and point of his arrival.
Blink, with explosion effects and some AoE =)
Sub-Zero
Drains the heat out of the target, dealing X damage to the target and stunning it for 4 seconds, as it turns into chunk of ice. Restores Y mana to the Mage. Has a 50% chance to cast Sleep on the Mage.
Since enemy hasn't turned into a hail of burning shreds and splintered debris, this spell is very boring for a goblin. Extremely boring.
Will think on other classes later.
Enjoy.
EDIT: added Mage