Invulnerability frames - i-frames - are periods during which a character cannot be damaged. They come from two completely different sources in these games, they behave differently, and confusing the two produces a specific and common class of death.
The two sources
Dodge i-frames are earned. They last about 0.17 to 0.19 seconds, they begin the instant you press the dodge, and they cost a stamina point. They are a reward for timing.
Post-hit i-frames are given. They last between 0.65 and 1.2 seconds depending on the game, they begin automatically when you take damage, and they cost nothing. They exist so that a single mistake cannot immediately become three.
Both make you immune to damage in exactly the same way. The difference is entirely in how you get them and how long they last.
Why post-hit invulnerability matters more than it seems
Without it, being hit in a crowd would be catastrophic. Four enemies overlapping you would deal four damage in the same frame, and a five-heart character would die instantly from a single positioning error.
With roughly a second of immunity, a mistake costs one heart and gives you time to move out of the situation that caused it. That converts a hit from a death sentence into information.
The practical consequence is that the moment immediately after being hit is the safest moment in the game. It is the correct time to walk directly through a crowd, reposition to open ground, or close on a caster you could not otherwise reach.
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The common death
The failure is dodging while already invulnerable. Post-hit i-frames last around a second; a dodge adds 0.19 seconds of invulnerability that overlaps with immunity you already had, and costs a stamina point for nothing.
Worse, the dodge has a cooldown. Spending it during post-hit invulnerability means it is unavailable half a second later, when the invulnerability has expired and you actually need it.
The rule: when you have just been hit, move rather than dodge. You are already immune, and the dodge is better saved for when you are not.
How i-frames are drawn
Post-hit invulnerability is shown by the character flickering - alternating between full and partial opacity at about six cycles per second.
Dodge invulnerability is shown by a ghost trail behind the character and by the accent colour brightening. The ghost is at the position you dodged from, which also makes the direction obvious.
Both are deliberately distinct, because they mean different things. A flickering character has already been hit; a ghosted one is mid-dodge.
Why the dodge window is so short
Dodge invulnerability lasts under a fifth of a second, and it would be easy to make it generous. The reason not to is that a long window changes what the game is.
Generous i-frames make the dodge a universal answer. If the invulnerability outlasts most attacks, dodging on reflex beats identifying what is coming, and the entire telegraph system stops mattering - the guard, the parry and the colour rules all become optional, which collapses several interacting systems into one button.
Keeping the window short preserves the identification step. A dodge answers the attack you dodged and nothing else, which means you still have to know what is arriving before you choose how to deal with it. That is the same reasoning behind front-loading the invulnerability rather than centring it.
I-frames and the combo
There is a scoring dimension to invulnerability that is easy to miss, and it points in the opposite direction to the survival one.
Post-hit i-frames arrive after the damage has already been done, which means your multiplier has already reset. That makes the window genuinely free in scoring terms - there is nothing left to protect, so it is the cheapest moment in the run to take a risk you would otherwise decline.
Dodge i-frames are the reverse. A successful dodge preserves a multiplier that is still running, which is frequently worth far more than the stamina it cost. In a game where the combo is near its ceiling, spending a point to avoid a hit is one of the best trades available, and it is why players who understand the scoring dodge more than players who are only trying to survive.
I-frames in the boss fights
The bosses in Ultimate Sword Arcade have attacks that would be unavoidable without a dodge - the Iron Warden's charge covers the whole arena in a straight line at 620 pixels per second.
That is why every game featuring an unblockable attack also gives you a dodge. The two mechanics are designed together: unblockable attacks exist to make movement necessary, and i-frames exist to make movement sufficient.
A useful test for whether a game is fair: does every attack have at least one answer? On this site, every attack can be avoided by distance, a dodge, or by striking during the open window. None of them require taking a hit.
Key takeaways
- Dodge i-frames last 0.17 to 0.19 seconds, cost stamina and are earned. Post-hit i-frames last around a second and are free.
- Post-hit invulnerability converts a mistake from a death sentence into information.
- The moment right after being hit is the safest moment in the game - use it to reposition.
- Never dodge while already invulnerable. It wastes the stamina and the cooldown.
- Flickering means post-hit immunity; a ghost trail means mid-dodge.
- Unblockable attacks and i-frames are designed together: one makes movement necessary, the other makes it sufficient.
Frequently asked questions
What are invulnerability frames?
Periods during which your character cannot take damage. In these games they come from dodging - 0.17 to 0.19 seconds - and from being hit, which grants around a second automatically.
Why am I immune after being hit?
So that a single positioning error cannot become four hits in the same frame. It converts a mistake into information rather than a death.
Should I dodge right after taking a hit?
No. You are already invulnerable for about a second, so the dodge adds nothing and puts its cooldown on exactly when you will need it next.
How can I tell I am invulnerable?
Post-hit immunity flickers the character; dodge invulnerability draws a ghost trail behind you and brightens your accent colour.
Is every attack avoidable?
Yes. Every attack on this site can be answered by distance, a dodge, or a strike during the wind-up's open window. None of them require taking a hit.
Why is dodge invulnerability so short?
Because a long window would make dodging a universal answer. If the immunity outlasted most attacks, dodging on reflex would beat identifying what is coming, and the guard, the parry and the colour rules would all become optional.
Is being hit ever useful?
The invulnerability afterwards is. Your multiplier has already reset, so there is nothing left to protect, which makes it the cheapest moment in the run to cross a crowd or close on a caster you could not otherwise reach.
Do i-frames make the games easier?
They change what the games measure rather than how hard they are. Post-hit immunity stops one positioning error becoming four simultaneous hits, and dodge immunity is short enough that it answers one specific attack rather than replacing the need to identify what is coming.