As well as bringing the end of Trials, the most recent update changed how Arcanes work. Arcanes were originally items rewarded by players for completing a trial, and you could only get one per trial per day (one for the Law of Retribution, one for the Jordas Verdict and one for nightmare variants). The only way you could use them was to attach them to a cosmetic of some sort, either a Warframe helmet or a Syandana. This is, thankfully, no longer the case!
Now, the only way to get an Arcane is to kill or capture an Eidolon. Each Eidolon drops a different Arcane depending on whether you kill or capture it, with the rarest ones being restricted to capturing the Hydrolyst. Arcanes being tied to Eidolons makes them a tad more accessible, due to the fact that there’s 50 minutes of night every 2 and a half hours. Most squads can at the very least kill the Teralyst, and a dedicated squad can capture three or four sets of Eidolons (9-12 captures) in that time. So you can get a lot more Arcanes than previously.
How you use your Arcanes has changed as well. Starting from Mastery Rank 5, two extra slots will appear on your Warframes in the Upgrade menu, and you can pick an Arcane to use in those slots.
Arcanes can be combined to give better stats. You need 3 of the same Arcane to reach rank 1, and you need 10 of the same Arcane to reach rank 4, which gives you the best stats. Arcanes have to be the same, you can’t combine different ones, but since you can use the same Arcane on every Warframe now, and they’re not tied to cosmetics, it’s much easier to get a whole set and use it.
A rank 4 Arcane also gives you one extra revive. Equip two on a Warframe and you get two extra revives.
Luckily, anyone who happened to have used Arcanes on their items have gotten them back, so they can use them as they please.
The question is though, are Arcanes worth using?
Honestly? No. Most Arcanes aren’t particularly useful. And almost all of them are useless when unranked. The chances on all of them are so tiny. For example, Arcane Victory, at max rank, gives you an 8% chance to regenerate 2% of your health for 8 seconds, when you get a headshot. Arcane Momentum’s unranked form gives you 10% chance to reload 25% faster on Sniper Rifles when you land a critical hit. That may scale up to a 40% chance to reload 100% faster but you need 10 Arcane Momentums to actually obtain that.
Even when you do have 10 of an Arcane, there are many far better Arcanes out there. Arcane Energize for example gives you a 10% chance to replenish energy to nearby allies when you pick up health orbs, but this scales up to 40%, and energy orbs are a pretty common drop. Warframes are always using energy, so it’s always handy to have something that gives you more energy. The downside to this is that Arcane Energize is a rare reward from a Hydrolyst capture.
Really, Arcanes are an old system that’s only somewhat been modernized and made more accessible. On the other hand, there’s still more work to be done for anyone to consider using the majority of Arcanes, and they take a good time investment to obtain.
But at the end of the day, Arcanes are something for veterans to work towards. So it doesn’t really matter if they’re mostly mediocre, it’s something to do, something to collect and a reason to go out and kill an Eidolon, outside of farming Sentient Cores for Focus.