A few things I've tested about Corvus

[laslax]

Abilities

Soul Harvest:
An anti ceramic ability that pops up to 20 Bloons. Mana gain is based on the type of Bloon you used Soul Harvest on, not if it pops it. Soul Harvest is the main skill you use to obtain more mana, so try to use it when you can, and focus on using Soul Harvest on ceramics and MOAB class Bloons.

Spirit Walk:
Useful to relocate Corvus while he is in Malevolence or Ancestral Might, and can also be used to land a Soul Harvest or Dark Ritual.

Dark Ritual:
Creates a damaging aura around Corvus that has 100 pierce and deals 1 damage. It is not a global ability, only damaging Bloons in Corvus’s radius like Malevolence. Dark Ritual does not move with you once you use Spirit Walk, and is also used to regain Mana, but it has a much longer cooldown compared to Soul Harvest.

Channel spells

Spear:
An extremely powerful damage ability. Terrible against single targets since Spears damage substantially increases with the more Bloons it can bounce on, up to its pierce cap.

10 mana drain a second

Aggression:
Increases attack speed of the spirit. Only good against single targets, and it is outperformed by Storm once you get it. Still, Aggression is cost effective if you want to be cheap with your mana.

5 mana drain a second

Malevolence:
Turns Corvus into a damage tower as long as Malevolence is channeled. Malevolence has 80 pierce, and deals 1 damage. At level 14 Malevolence deals 2 damage, and +1 ceramic damage.

Spear will be fired in Corvus's range instead of being global range with the spirit.
Storm will fire from Corvus, which doesn’t seem very useful.
Repel gives the knockback shield to Corvus.
Frostbound gives Corvus a small frost aura, freezing any Bloons around him.
Echo, Haste, Trample, and Ember do nothing.

6 mana drain a second

Storm:
Storm specializes in single target damage. Spear will outperform Storm against grouped Bloons, but you can use both if you need it. Storm is also okay if you don't have Ancestral Might, or want to save it.

15 mana drain a second

Cooldown spells

Repel:
Pretty bad on its own when it doesn't affect MOABs until it reaches level 12, but it will still combine well with Frostbound. The Repel and Frostbound combo will push everything back to the entrance with its infinite piercing until there is a Bloon it cannot affect, or the duration runs out. Not very effective on multi lane maps.

Echo:
A very good spell that duplicates your spirit. Combines well with practically anything, but try to use it with powerful spells like Ancestral Might and Overload.

Haste:
Keeps the spirit up with spaced Bloons, and might be useful for multi lane maps.

Trample:
Basically a Sauda sword charge. Its only good against Bloons until you get level 10 and 19 where it can be effective against MOAB class Bloons. Echo will send your spirit at the entrance and exit. At level 10 Trample will now one shot fortified ceramics and can be used to clear ceramic rounds. At level 19 Trample will now one shot fortified ceramics in Freeplay.

Frostbound:
Extremely powerful against Bloons, but terrible against regrows. There is no pierce cap with Frostbound, and it works with Echo, Malevolence, Ancestral Might, Haste, and Trample. At level 9 Corvus can slow down MOABs with Frostbound. Bloons affected by Frostbound are frozen and cannot be popped by sharp attacks.

Ember:
Generalist skill useful for regular and MOAB class Bloons. Combos well with Frostbound to keep Bloons in Ember. It's cheap, and is a good option if you don't have much mana.

Ancestral Might:
Your most powerful Spell. Has the same combos as Malevolence, but also works with Echo to double the ability. At level 7/13/20 Ancestral might deals 100/250/500 damage and has 30/38/38 pierce.

Overload:
Oneshots fortified MOABs, BFBs, and DDTs. The explosion only deals with one layer, but it's a good nuke button that you can double up with Echo. Usually you want to save Echo for Ancestral Might, but if you're doing an Echo combo with Ancestral Might, Echo will have enough duration to be used with Overload. After using Overload, you can resummon your spirit instantly by casting Recovery.

Support Spells

Nourishment:
An okay option to power level Corvus for essentially free. A good tip is to save Soul Harvest or Dark Ritual to regain your mana after casting Nourishment. Recovery is a good spell to use to regain Nourishment in order to level Corvus faster.

Soul Barrier:
Gives temporary bonus lives based on your mana after you cast Soul Barrier. At base level Soul barrier caps at +400 lives requiring 440 mana. When Corvus reaches level 9 Soul Barrier is based on max mana.

Vision:
Decamos anything your spirit hits, and is best combined with an AOE attack like Spear. Good enough to deal with DDTs if you have at least one decent camo tower with Corvus.

Recovery:
Stops the spirit from attacking to increase CD speed. Recovery immediately stops when all spells are back on cooldown. Recovery does not prevent Corvus from using their abilities, and it is best used to regain Ancestral Might, Echo, and Nourishment. Corvus can only gain mana from his abilities while Recovery is active.

[laslax]

Also, Corvus seems to work really well with middle path druids. I don't know why they work so well together, but Corvus practically gets infinite mana.

[Revalopod]

Originally posted by laslax:

Also, Corvus seems to work really well with middle path druids. I don't know why they work so well together, but Corvus practically gets infinite mana.

Having top path druid for blowback is really good (I always like to use it).

[laslax]

Originally posted by Revalopod:

Originally posted by laslax:

Also, Corvus seems to work really well with middle path druids. I don't know why they work so well together, but Corvus practically gets infinite mana.

Having top path druid for blowback is really good (I always like to use it).

Yeah, I like top path too. Druid of the Storm is basically Downdraft for lazy people like myself, and Superstorm seems really good if you can afford it. I know blowback is good with Spike Factories, but they seem to have a little anti-synergy with Spiked Mines, and I like Spiked Mines.