According to the UK server spoiler thread, it's the Great Challenge, and will include a heart fight. I'll leave it to someone who has the full info to post it. Though the main divine gives a Hera pack apparently.

One thing I noticed: they say in the Hearts fight there will now be 3 'sessions' a day when you can get a maximum number of hearts each session. No more details than that given, but I'm really pleased. Ever since I did my 1st Hearts last year, every fight I've suggested they do something so it isn't all day and night with no time to sleep properly if you want to compete. I suggested they reduced the minimum time between UFOs and had an (advertised) maximum number per day so that people could schedule when they wanted to be on or had set time periods each day. So maybe they listened on that!

And quess what. They promissed a Horn of plenty as a reward after 7. day. But. BUT! You need to use this HoP immediately after finishing two objectives in last day, so you can't open it later from inventory. There are also objectives as a "Equip the -one random colour- 2 ** bandage to horse" or "Buy one horse from sale." So, new players say how great it will be to get passes daily for free, but it does not pay off. There are pass losses after finishing all objectives.

I give the picture of the oldest Yggdrasil to CZ Howrse

Essentially, yes it will be another UFO event. However, this one will be tied in with the Great Challenge which, if my understanding is correct, will limit the number of UFOs we can catch in each 8 hour session depending on how many horseshoes we collect, up to a max of 4 every 8 hours.
There is also an option to replace your UFO with another one using equus if you don't like what you catch, which is something we haven't had before. We haven't had bonus items before either, which will allow you to gain extra points when sending the gift to another player.

So the basic idea is the same - log on, catch UFOs, either keep them to get the prize or send them on to climb the ranking - but there are some tweaks to it.

I thought we were able to get the new Love Divines in the horn of plenty. I'm pretty sure I saw someone a couple pages back say they were. Did it change?

added to the game with the love fight in February, so I believe, that they'll be in HOP's, when this promo ends. But I'm not sure.

bezo93's post with the info for the promo that will happen in February seems to suggest that the Love Divines will be available in Golden Fleeces, instead of the horns of plenty

The New Celtic Divine will be in the Fleeces for the Great Challenge.

Love horses are always offered in Horns of Plenty during the St Valentine's weekend.

The new Love divines are prizes available in the Heart fight, but the new divine Aengus is the one available in GFs (as well as being the prize for the top 5 Heart Fight winners). We don't have any official confirmation that the Love divines will be available in HoPs (unless I've missed it) but as that is what has happened in recent years, I presume it will be the same this year, too.

The GF promotional offer this time is a divine dust multiplier, so the more multipliers you have the more dust you get when opening GFs. The first one is x1.5, the second x2, and I don't think anyone has got further than that yet.

the mazes, right?

what horses will be needed for each short cut

I'm a little confused on how the hearts fight is going to work this time. The sessions are going to be a time frame during the day in which we catch UFOs meaning no more catching them at night?

Will we know what the max number of UFOs are? What exactly are the bonus items supposed to do as far as selecting them for the UFO?

Sorry for all the questions I'm just a bit lost.

The day will be split into three 8 hour sessions, so the promo will still be running 24 hours a day. How many UFOs can be caught during each 8 hour session will be determined by how many horseshoes we collect: if we only collect enough to reach the first threshold, we will get 1 UFO per 8 hours; for the second threshold we get 2 UFOs per 8 hours; third threshold 3 UFOs; and fourth (and final) threshold 4 UFOs per 8 hours. We usually manage to reach the third threshold during the GC on this server, so I would expect to be getting at least 3 UFOs per 8 hours.

We haven't got around to testing the Hearts Battle yet - we are still on the GC phase at the moment - so I'm not sure if the UFOs will be evenly spaced out over each session (so if we reach 4 UFOs they will appear roughly every 2 hours, or if we reach 2 UFOs they will appear roughly every 4 hours) or if it will be more random.

My understanding of the bonuses is that when you choose to throw your UFO to another player (which gives you points towards the ranking) you will be able to use the bonuses so throwing that UFO gives more points. E.g. If throwing AP gives 10 points, then using a bonus item will make that AP UFO give you 18 points instead. The more bonus items you use at once, the more points you get for that UFO. However, using several bonus items at once will give fewer points than using those bonus items separately (using 4 bonus items at once gives 15 bonus points while using 1 bonus item gives 8 bonus points - if you used four bonus items separately you would get 32 bonus points altogether).

I'm still a bit confused over exactly how it will work myself but, hopefully, it will be clearer once the Hearts Battle starts and we can test it to see exactly how the changes work.