I just stumbled over something odd in the Horse companion's support benefit. It looks like the rules are not intended as written.
It says:
"Your horse adds momentum to your charge. Until the start of your next turn, if you moved at least 10 feet on the action before your attack, add a circumstance bonus to damage to that attack equal to twice the number of damage dice. If your weapon already has the jousting weapon trait, increase the trait’s damage bonus by 2 per die instead."
So first of all (as another player pointed out to me) it seems very likely that this should only apply if the character is actually mounted, because otherwise it makes no sense out of several reasons.
Secondly this benefit per RAW applies to all attacks including spell attacks. Is that really intended? Intuition says otherwise.
I thought about some pros and cons, although I am pretty sure that this is just a mistake.
Arguments against RAW interpretation:
1. Animal companions usually apply to weapon attacks. Also it makes no sense that riding on a horse adds momentum to a spell.
2. As written here spells would get one additional damage per damage die. This is both ridiculously powerful and also pretty random: Spells usually have more damage dice than weapon attacks and there are huge differences between spells. There are spells that get one additional damage die every two levels and there are those that add more than one damage die per level. Admonishing Ray for example deals 2d6 damage per level. The expected damage is 7 damage per level. With the benefit it's 9. That's 28%.
If someone attacks with a ranged attack like a shortbow (1d6) of course damage would also increase by 28%, but the additional damage in total is still lower because the spell still gets more damage dice per level. You can usually make more strikes than spells each round but the support benefit counts only for one of them.
Arguments pro RAW interpretation:
1. Horses are the only common mount companion and mounts do NOT only make sense to non spellcasters (or even only to melee characters). Additional mobility is also helpful for spellcasters or ranged attacks in general. It seems a little unfair that weapon fighters get a pretty strong support benefit and casters just don't get anything if they have a mount.
2. The rules clearly say "attacks". There are a lot of other companions whose support benefits are explicitly restricted to strikes. I wonder why it should have been forgotten only for this companion and if there is any reason why it says "attack" and not "strike" here. Possibly it was supposed to work for another attack ability which was not a spell?
Would be great to have some clarification on that.