Honestly it's not that bad. Just fundamentally deeply silly on a structural level. The text gets in the way of making sense of the ability. But what leaps out to me is that it is an ability only relevant to out and out munchkins who have had their character power levelled.
The effects of Gae Bolga aren't that fiddly. OP, yes. Spammy in the sense that that's almost the only thing you ever do after getting the ability, yes. Fiddly, no.
- Make a spear attack and multiply the damage by your level
- Give up your action on your next round
- Take a fixed AC penalty (at least -3) when doing it
There's nothing there you couldn't easily put into a 4e power block. And tweaking slightly it would read something like
Gae Bolga
Ranged Weapon
Requirement: You must be wielding a spear
Attack: Weapon vs AC
Hit: (1[w]+Dex)*your level
Effect: You are stunned until the end of your next turn
I've seen worse. Much worse. And I think it comes from an edition that gave weapon vs armour type modifiers.
The prerequisites aren't too complex either. Just something only a power levelled munchkin will ever do.
Prerequisites:
- Dex 17 (easy to check)
- Spear Proficiency (easy to check)
- Spend six weapon proficiency slots on the technique
And it's that last one that makes me think that no human in the history of ever has legitimately acquired the ability in play.
The reason is that you just didn't have that many weapon proficiencies, needing a minimum of seven to qualify (one for the spear and a further six for the technique)
- Fighters only gained four weapon proficiencies plus one every three levels. So you already need level 9 to qualify.
- Much of the point of being a fighter was Weapon Specialisation for +1 to hit, +2 damage, and an extra attack every other round. This cost a proficiency and I don't believe in any fighting type that doesn't take it. We're up to level 12
- If we're going outside the PHB (as we are) there's also shield specialisation for extra AC (a nearly as obvious pick) and weapon mastery for extra to hit and damage with your spear, both of which cost proficiencies. Hard to pass up for anyone actively fighting for their lives.
- The spear in AD&D was just an objectively bad weapon, doing less damage than the longsword while being far worse at being thrown than darts. And the magic items tables were deliberately heavily rigged towards longswords.
So basically you had to both have a 17 Dex and put up with a dozen or so levels of sucking in order to become a ludicrously broken one trick pony that only acted one turn in two. This sort of ability is only really of interest while reading or to munchkins playing games that start at ultra high level.
And, to be honest, these abilities with waterfall development over such an absurd level range shatter any feeling of realism I have. Cuchulain was powerful - but he was anything but the one trick pony a technique that costs six weapon proficiencies would make him. Bad detail makes the world less real.