Hi there end game necro one trick here with multiple trial and dungeon trifectas as cro on all classes, along with too many hours in IC on cro so you have background for my experiences
First - PVE tank cro
Tanking on a cro is in a rather good spot gameplay wise with their weakest points being surviving rapid burst such as xalvaka heavies on HM along due to lack of effective shield or block mit with poor stam sustain (rarely having bar space if well optimized to equip mortal coil or Mystic siphon), otherwise high one of the best survivability's
Group comp wise cro is really only there to apply the now no longer unique major vuln and build saxheel colo fast, rarely as a class really good at living hard hitting dots, they offer no unique minor buff like all other classes can
Bone tyrant treeline: Ravenous goliath is the morph for 99% of builds with the other only being for niche bash builds that now have to spec into damage as that damage doesnt scale with health or armor like bash or the colo damages does. only other thing to say is feels bad cant build ult while in ravenous but can see arguments for being and not being able to such as corrosive and magma being similar situation
Scythe - blue mid tier burst heal that also has the downside of have to be facing enemies, but is very cheap helping on mag sustain and worse whirling blade dps option, receiving indirect nerf with status effect change
armor - free chain is nice most the time but mostly only used over balance for passive uptime and corpse, sustain morph only used in pvp so it doesnt proc stun CD at inopportune times
Bitter harvest - extreme strong in pve and pvp ability, feels bad casting a 2nd times removes heal duration if it was longer, ulti gain morph far superior far pve carries the class in trash and the major protection morph is rather strong in pvp
agony totem - a rather useless skill that is out classed and rarely worth the spot, the other morph is functionally useless
empowering grasp only used to snare trash with vateshran snb pull, the longer snare morph changes nothing in pvp as just break free or rol ldodge and in pve snaring once is enough most the time
Passives: death gleaning feels bad have to have bone tyrant on but overall useless as cro sustain is already insane, disdain harm strongest part of cro kit for tanking, health avarice, just a worse dk burning heart passive that gets 12% healing taken for 1 cast vs 2% on that bar only, last grasp forgettable rarely has impact
Tanking TLDR - over all good, carried by passive, most morphs useless counter part, some abilities useless
Healing on a cro is more or less dead and gone now in meta comps with the removal of empower effecting light attacks, the actual healing power of necro is rather weak too, the iconic class heal that consumes a corpse too use is rather clunky in the kit to use as either have to pre cast mender for a corpse or run blast bones loosing more hps casting a non heal every 3-5 seconds or so to keep the hot uptime
Living death treeline: animate blastbones is used in some fun burst combos pvp, other morph is used a crutch for bad groups in pve, a barrier would result in better results most times
resistant flesh - the only morph of the ability, very strong but the resistance only lasting 3 with the defile last 4 feels bad in pvp, as its debuff last longer than its buff, the other morph is a waste of a corpse
expunge and modify - niche use in pve otherwise just on troll tanks in pvp, rather useless overall, quite boring design of purge self and do nothing else effective
life amid death - bread and butter heal of the class - if have corpses very strong for 5 seconds, the actual hot on it is rather weak and casting again is often better, the 5 seconds duration makes it hard to upkeep with the need of corpses, the longer lasting morph will rarely have corpses for full duration and even if it does rarely will you be in place for 30 seconds, the purge morph has the problem of conditional purge timing when in pve purges need to be fast, in pvp its a plague break enabler
spirit mender, slot bonus for tank/heal/pvp for a passive and or 10% unnamed mit. the actual heal is rather weak
restorative tether has the tank/pvp sustain morph with a negligible heal attached and the healer morph for a free hot and slot bonus only ran as no other good option available as healer
Passives: curative curse - overall useless in pve as rarely do fight have a debuff on you with good uptime and in pvp jsut counter acts the minor defile res flesh puts on you, near death experiences pvp relevant only as crit healer builds are not consistant to be good, corpse consumption mid tier ulti gen of ~0.8 a second slightly stronger than nord passive lowest of ulti gen passive of rest of classes but very easy to proc, undead confederate lots of good sustain forces have archer or mender as blast bones too inconsistent
Healing TLDR - garbage, too clunky and and slow, most abilities both morphs viable only 1/2 unusable, no good passives to boost healing or reason to take cro healer over any other class
DPS on a cro - cro is only brought as a dps to apply EC and Vuln if another class could do so or didn't have to give up another set for a vuln source would never be seen in optimized groups again
Dealing damage on cro is too stationary, slow and clunky, half the class abilities often fail to cast far to frequently, the class has no major or minor buffs so either loose 3 ability spots for savagery both bars and a source of degen or run wep/spell power pots limiting the play style even more, which hurts even more since cro main purpose atm is to build ult and they loose 3 dots they could run for ulti pots nerfing damage even further. The rare parse cro also feels bad as you have to do far more to receive far less than other classes, cro also lacks a unique damage buff for a flat amount of damage gain before multipliers, along with no good class spammable. Venom skull is only worth while to cast every 3rd cast but with the rotations the venom skull is cast in bursts so even that ability just feels bad to have 4 or so low value cast before having to go back to dots and bb rotation
Grave Lord skill line - Glacial colossus only morph of the ult as its far superior
Venom skull - worse variant of dk whip, bouncing skull worse version of force pulse
Blastbones - blue blastbones strong ability feels horrible if looses target or gets stunned, blighted blastbones very much worse version of stalking blastbones damage type and damage re sult in minmum loss of 10% plus ~9 from encratis and engulfing effective fire damage in pve and 10%-20% + 13%-20% fire damage to vampires in pvp massive damage loss using the morph overall
Boneyard - good if consumes a corpse which often misses if not centered on corpse, mage/archer stand to far away to cast directly on feet and the corpse to be in range if stationary, have to cast behind yourself or wait for blastbones loosing up to 4 gcd of uptime if you dont want to cast without buff, both morphs goods unnerving better for group overall
skele archer - summon bonus for the regen passive bad damage, other morph use a different ability if you want cleave damage
mystic siphon only used to proc shock damage for EC since pet damage doesnt count for that, detonating siphon the far superior morph with the secondary part only relevant in stationary fights
Passives: reusable parts- blast bones cost 1k now undeed sustain, death knell - pretty mid execute passive as is an all or nothing at 25%, dismember - free pen, rapid rot enables dot build deters spammable build
TLDR only there to apply major vuln or EC, too stationary reliant and lacking buffs and unique weapon damage buff common in all other classes
PVP for cro - either colo bomb with darkconvergance or be a strictly worse dk just bad with lack of sticky dots, reliable stuns, sticky debuffs, reliable class spammable, class sourced buffs resulting in struggling for bar space and always missing out on something
How current week 1 upcoming changes effect Cro
Blast bones change, nice for tank for more consistent corpses for ulti gen, worse for healer as not corpse placed on self instead of near boss were dps should be and the other morph cost stam which is more limited as a healer, dps either huge nerf for current playstyle resulting in blast bones hitting for 10k+ less every cast or loose all cleave damage and ability to damage in mobile fights entirely. With blue blast bones venom skull or bouncing skull is a must have so good aoe spamamble are gone along with blast bones itself removing most cleave damage then the lack of frequent corpses also means boneyard or siphon will result in less effective boneyards or downtime on siphon, or a complete wasted cast of buffing again early to gain no damage
passive buff - a nothing change overall buffing mid tier damage results in slightly higher mid tier damage
status effect changes: blighted blast bones is being indirectly nerfed by this change as its now less effective defile , ruinous scythe in hit hard by the hemorrhage change resulting in damage per cast being less, and its not expected for any current cro build to cast scythe every 4 seconds to keep up the dot, and scythe cant even be used with the blue blast bones morph as its not effected by the buff at all, being a wasted cast or out classed by venom skull