5. Sand KING " Sand STORM "
The 5th place opens the Sand King. Not because of his ultimate, but 2nd skill "Sand Storm". However, you might not know how much damage it does. Sand Storm deals 100 DMG and it lasts 80 seconds. In other words, this spell does total 8000 DMG ! This is one of the greatest spells, but the chances for the hero to stay there for 80 seconds is ZERO . That's why Sand King took 5th place.
4. Razor "Eye of the STORM"
The 4th place is dedicated to Razor's ultimate "Eye of the Storm". It lasts 30 seconds and with Aghanim's Scepter lightning storm strikes out 3 times per second 62.5 DMG each. At level 16 it can deal total 5300 dmg and it is really powerful. However, it deals slowly, by small portions and changes target easily. So Razor with his ultimate is at 4th place.
3. Crystal Maiden "Freezing FIELD"
The best 3rd spell is Crystal Maiden's ultimate "Freezing Field". For enemies within 485 radius Freezing Field with Aghanim's Scepter deals about 6000 DMG slowing movement and attack speed. That's why it is common in the game Double/Triple/Ultra kill and RAMPAGE. I gave 3rd place , because it is easy to escape from the radius 485 of Freezing Field. If you make combo with Magnus or Treant protector it works pretty good.
2. Lich "Chain FROST"
The 2nd place is "Chain Frost". Releases an orb of frost that bounces up to 10 times, dealing total 4600 DMG and slowing enemy units. The first target is mini-stunned. Aghanim's Scepter increases damage, casting range and removes bounce limit. After bouncing 60 times, Chain FROST loses its vision and stops playing a sound when bouncing on non-hero units. If enemies are too close to each other it deals huge damage in a short time.
1. Witch Doctor " Death Ward "
THE MOST POWERFUL SPELL in DOTA 2 is the Witch DOCTOR's ultimate "Death Ward". Witch Doctor summons a deadly ward to attack enemy heroes. It attacks every 0.22 seconds and lasts 8 seconds, which means it can attack 36 times. It can deal up to 4320 ( 5400 with Aghanim's Scepter) damage to a single hero. When all attacks and bounces hit, it can deal up to 8640 ( 27 000 with Aghanim's Scepter ) damage !!! LOOK at it GO ! ! !
It is scary when you have mega creeps in their base and 2 lich ults start jumping around.
WD ult is heavily reduced by armor by the time you get aghanims
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Jokes aside:
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Ok, jokes aside. There is no such thing as: "The most powerful spell in Dota", because everything is situational. Of those you listed, I can quickly think of some abilities, that are more powerful [situationally :)].
Please, your blog may be fun, etc., but it's not some great piece of knowledge.