Learn Spanish (Latin America): Iba a salvar el cono, pero se iba desmoronando rápido. - I was going to save the cone, but it was crumbling fast.

The structure iba a + infinitive (the imperfect of ir + a + infinitive) translates to 'I was going to do something'. Just like in English, expressing a past intention this way usually implies that the action never actually happened. Here, the speaker intended to save the cone, but the crumbling prevented it.

Wait, the verb iba is used twice here. Are they doing the same thing?

No, they serve completely different functions! The first iba is part of ir a + infinitive to show an unfulfilled intention ('I was going to save'). The second iba is part of ir + gerund (iba desmoronando). This structure emphasizes a gradual, ongoing process, meaning the cone was falling apart bit by bit. If they had used estar + gerund (estaba desmoronando), it would just mean 'it was crumbling' without that gradual emphasis.

Why is there a se before iba desmoronando?

It belongs to the pronominal verb desmoronarse, meaning 'to crumble' or 'to fall apart' on its own. Without the se, the verb desmoronar is transitive and means to cause something else to crumble. The pronoun se can go before the conjugated verb (se iba desmoronando) or attached to the end of the gerund (iba desmoronándose).

Why use rápido instead of the adverb rápidamente?