Some skill gems that'd be cool (add your own too)

Throw Monster - Melee only. Picks up and throws a monster directly away from the caster (like knockback, but not useless...well, kinda), dealing damage to both it, and creatures in the line it is thrown. Boss can't be thrown. (as a bonus, perhaps smaller enemies would be thrown farther?)

Ray of Assimilation - In a straight line, deals slowly increasing damage (up to a point), killing enemies releases a taunting call at the point that the slain enemy was killed (calling more enemies in), and increases damage (uncapped). This damage increase remains until you stop casting. Increased AoE would increase the AoE of the taunt and of the ray. Not a projectile.

Throw Fish - consumes a caught fish in you inventory to deal massive damage in a small AoE if it hits its target. Else you wasted food.

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As well, there are some gem-specific support gems that'd be nice. They'll never be implemented because support gems are supposed to be hyper generic so to fit with everything, but adding some variety to specific gems without directly boosting there powers could be nice for this game.

Thunderstorm - supports Arc and Lightning Nova (or whatever it's called) only. Reduces damage. Whenever a target is hit, a secondary arc fires and hits one target. This secondary arcing doesn't proc thunderstorm. A single cast may proc multiple thunderstorms, and they may hit the same enemies.

Lightning Rod - supports Arc only. Arc can bounce back to you, if no other targets exist (even if you would normally be outside of it's range). If it does so, it resets the counter for what targets it already hit (ie. if it bounces off you, it can hit the same targets again)

Icy Needles - supports Freeze Mine only. Ice Mine may never freeze. It's effect, however, stays on the target while the duration lasts. Has a duration scaling with gem level. Perhaps increased quality gives + to the resistance drop.

Portal To Hell - supports the Portal gem only. In normal zones, any portals created from the use of Portal sends you to a random location in a random area of the act. In the end game zone, if you have maps in your inventory, it consumes a random map and opens up portals to a random map area of equivalent level, but you do not know what mods are used (from 1-6 mods can be generated).
In both cases, all enemies' enchantments are hidden, and power has been increased. Loot, likewise, has been increased.

Must be trolling, cause none of those gems look cool. Except maybe ray of assimilation, the taunt on corpses looks interesting.