The way you have it worded, you'd first remove one evolution counter, then two, after which it gets three again, which you remove to turn it into ultimate form. You don't need the counters. Checking for the right creature types is restrictive enough. Nor does unblockability need a keyword other than "unblockable." Also, this creature is a 5/5 spider on turn 2 in mono G or mono U. Great concept, but not well thought out. 5.5/10
(B/R)Hellfire Acolyte
Creature - Human (R) (B/R), Sacrifice another creature: If Hellfire Acolyte is a Human, it becomes a 3/3 Devil creature in addition to its other types. (B/R)(B/R), Sacrifice another creature: If Hellfire Acolyte is a Devil, it becomes a 6/6 Demon creature with flying in addition to its other types. (B/R)(B/R)(B/R), Sacrifice another creature: If Hellfire Acolyte is a Demon, it becomes a 9/9 Legendary Avatar creature with flying and trample named Archon of Hellfire in addition to its other types.
Next: A 1 CMC Instant or sorcery that exiles itself.
Add three mana in any combination of colors to your mana pool. Spend this mana only to cast green spells or activate abilities of green sources. Exile Dank Ritual
Instant (U)
Put a 1/2 green Spider creature token with reach and a 2/4 black Spider creature token with reach onto the battlefield. Then, if an opponent controls more creatures than you, creatures you control gain deathtouch until end of turn.
Legendary Creature - Avatar (M)
When Avatar of Generation enters the battlefield, exile the top X cards of your library, then you may put a creature card from among them onto the battlefield. If you do, repeat this process.
4/4
Creature - Serpent (C)
Tidal (At the beginning of your upkeep, if this has no +1/+1 counters on it, put a +1/+1 counter on it. Otherwise, remove all +1/+1 counters from it.)
Reef Predator can't attack unless it has a +1/+1 counter on it.
4/4
Instant (C)
Counter target spell that has no targets.
Land (R)
T: Add to your mana pool one mana of any color a land you control could not produce.
***
Spellcharged Weird 1U
Creature - Weird (U)
Hexproof
Spellcharged Weird enters the battlefield with a +1/+1 counter on it for each spell cast after it this turn.
2/1
Actually, no, since armadillo's lifegain effect stacks but lifelink doesn't.
Sorcery (U)
Populate, then populate again.
(B/R) Hellfire Acolyte
Creature - Human (R)
(B/R), Sacrifice another creature: If Hellfire Acolyte is a Human, it becomes a 3/3 Devil creature in addition to its other types.
(B/R)(B/R), Sacrifice another creature: If Hellfire Acolyte is a Devil, it becomes a 6/6 Demon creature with flying in addition to its other types.
(B/R)(B/R)(B/R), Sacrifice another creature: If Hellfire Acolyte is a Demon, it becomes a 9/9 Legendary Avatar creature with flying and trample named Archon of Hellfire in addition to its other types.
Next: A 1 CMC Instant or sorcery that exiles itself.
Sorcery (R)
Add three mana in any combination of colors to your mana pool. Spend this mana only to cast green spells or activate abilities of green sources. Exile Dank Ritual
Instant (U)
Put a 1/2 green Spider creature token with reach and a 2/4 black Spider creature token with reach onto the battlefield. Then, if an opponent controls more creatures than you, creatures you control gain deathtouch until end of turn.
Creature - Skeleton (C)
Protection from tokens.
The Pawnsbane don't fall to any run-of-the-mill soldiers.
1/1
Land - Desert (U)
T: Add 1 to your mana pool.
T, Sacrifice a land: Put a 1/1 colorless Sand creature token onto the battlefield.
Creature - Elemental (R)
Bloodrush - RR, Discard Krark-Clan Sparkform: Target attacking creature gets +5/+0 until end of turn.
5/0
Legendary Creature - Avatar (M)
When Avatar of Generation enters the battlefield, exile the top X cards of your library, then you may put a creature card from among them onto the battlefield. If you do, repeat this process.
4/4
Artifact (C)
WU,T, Sacrifice Hushing Stone: Counter all triggered abilities.
Creature - Serpent (C)
Tidal (At the beginning of your upkeep, if this has no +1/+1 counters on it, put a +1/+1 counter on it. Otherwise, remove all +1/+1 counters from it.)
Reef Predator can't attack unless it has a +1/+1 counter on it.
4/4