The most powerful (not "top") cards should be game warping, here they are:
Obliterate/Jokulhaup/Decree of Anilihilation
Armageddon type spells
A few others that are game-warping but to a lesser degree
Tooth and Nail
Myojin of Night's Reach
Not necessarily game warping, but mana engines are the enabler to game-warping plays:
Priest of Titania/Wirewood Channeler
to a lesser degree:
These aren't game warping cards but adds resilience to potential game warping plays as well as provide added utilities:
All Sun's Dawn
Here are the dubious inclusions in your original list:
Wardens: These can be good if your deck has a way to generate huge amounts of creatures such as Infernal Genesis
but most decks just play these in their token decks and have little utility besides gaining a bunch of life and they usually don't matter late in the game when your opponents are casting game breaking spells and you are still only making tokens.
Congregate: Not enough of a back-breaking life gain spell. We want quality things like beacon of immortality
and ancestor's chosen
or continuous sources of life gain like clearwater goblet
and miren, the moaning well
Grand Arbiter: It is a shame its a creature and only good if you run heavy protection and ideally, thats only counterspells. If you run the number of counterspells that is needed to protect the arbiter, you are running way too many to be a good multiplayer deck.
Avatar of Woe: You'd have to include a bunch of other creatures like visara
, kamahl, pit fighter
, and callous oppressor
(which is usually better than avatar btw). They have the vulnerability as a creature and avatar has the added weakness of being a sizable threat.
verdant embrace: Too many inherent vulnerabilities to be classify as good. Dies to enchant hate, creature hate, and bounce.
nezumi shortfang: the 1/1 stat makes it easy to kill. Not an efficient source as a disruption and takes too much time to turn into a rack.
rith: If you want to produce saprolings, there are better ways like selesnya guildmage
, sprout swarm
ixidron: It can the biggest creature sure but it will eventually get smaller and can be gang-blocked. Also, wrath and final judgement
type cards deal with creature swarms more efficiently
lurking jackal/skirge: only activate late game by which time, has too little effect
Hidden creatures enchantments: I am quite skeptical about these because they require certain things to happen to activate and then still die to creature and enchantment hate. Also, in multiplayer, they may still be too slow even though they are efficient.
psychic allergy: land sac=bad times
baru: small overrun ability. Try Kamahl, Fist of Krosa
nihilith: 4/4 fear is pathetic even if u only spent 1 mana to get it out.
thundermare/timbermare: Its only 1 turn and u deal 5 damage (all your creatures are tapped too) out of the multiple of 20 damages you have to deal.
magus of candelabra: I can see using this to effectively create shared mana for your teammate but candelabra of tawnos
is strictly better, being not a 1/1 and not effected by summoning sickness.
Black Vise/Rack and all their cousins: Well, only some of them. Wheel of Torture is probably the only one I like. Everything else has some flaw that makes it less attractive. Also, the enabler for this are the mass discard like pox
so the credit should go to those cards.