This is a flat damage increase, and is probably the one most players will end up taking as it just works in all situations. The low cooldown plays into Arcane's new frequent mini-burn playstyle. The issue comes with spells that are treated as separate hits, like Arcane Missiles. These spells consume multiple stacks (one cast of Arcane Missiles will take every stack of Radiant Spark), and spells with different travel times (Arcane Blast/Arcane Barrage) also interfere with the debuff. That makes it awkward to play ‘correctly’ and line up your biggest spell with the fourth stack.
Unfortunately, considering the general usefulness of Radiant Spark, the Kyrian signature ability is by far the weakest of any Covenant. While others gain shields, targeted teleports and movement speed increases, Summon Steward essentially boils down to Fiala della Serenità
: for all intents and purposes a glorified Healthstone. The healing will be nice, and the bleed and disease dispel could come in handy if you have already used Blocco di Ghiaccio
; however, the circumstances where Phial will be invaluable will be few and far between compared to other, more universally useful Covenant abilities.Venthyr
This spell will almost never get its full value in PvE, as NPCs rarely cast frequently enough to consume all three stacks, plus you generally should be interrupting their spells anyway. The cast speed slow effect, while useful, makes proccing the damage, root and silence at the end even less likely. In addition it appears to just simply not work on most PvE bosses, and in PvP begs to be dispelled. An extremely disappointing ability with niche uses, which will not even work on the majority of dungeon mobs.
Probably - unfortunately - the star of the Covenant signature abilities. A targeted, 35yd teleport with a 1-minute cooldown will enable many dungeon skips and the ability to avoid raid mechanics. Some players in the alpha have even said that not going Venthyr would be effectively trolling other party members in dungeons. This type of movement is almost universally valuable and it's hard to think of an occasion where it'd be useless, so it's a shame to see Mages forced towards our weakest Covenant if we want to be able to use it.Necrolord
Another contender for the default option, this ability has the advantage of having a use in cleave situations, although the cooldown is much longer than Radiant Spark's. However, Fireball and Frostbolt are not particularly hard-hitting, so the Necrolord Covenant will be less attractive for the vast majority of Mages who feel that they need to switch specs - which, again, pushes the entire class towards Kyrian for Radiant Spark or Venthyr for the teleport.
This extra self-survivability is fantastic, but the 4-second channel is a real downer; Arcane hardly needs another long cast-time ability to fit into its attempts at dodging mechanics. Even with a reduced cast-time, this one is hard to justify taking compared to Door of Shadows or Soulshape.Night Fae
Aesthetically this is by far the best-looking Covenant ability, but that’s where the attraction ends. Being forced into melee range is traditionally unhealthy for casters (we’re treated as valid targets for ranged mechanics no matter where we stand), and standing still for six seconds while the spell channels is even worse; Shifting Power takes the worst aspect of Fleshcraft and amplifies it by 50%. Coupled with the fact that it only ticks every 1.5 second, for three seconds of cooldown reduction per tick (so four ticks), compared to a more frequent and smaller reduction (say, 1 second of reduction every 0.5 seconds) and the cost of interrupting the spell becomes even higher. On top of all that, at just 12 seconds of reduction per full channel and a 45-second base cooldown, that is a LOT of time taken out of the Mage rotation.
Teleports are universally valuable, and while it might not be as strong as Door of Shadows this is a strong second-place option, especially as you can cast while shapeshifted. Three Blinks in the 12-second duration will enable easy repositioning and the ability to dodge some nasty mechanics. The minigame of collecting new forms is also cool! Sadly, again, this is linked to a really poor class ability.