Learn Portuguese (Portugal): Se o dragão fosse mais pequeno, voava melhor. - If the dragon were smaller, it would fly better.

In this sentence, fosse is the Imperfect Subjunctive form of ser (to be), meaning 'were'. The verbs ser and ir (to go) share the exact same forms in this tense, just like they do in the simple past tense. You have to tell them apart by the context of the sentence!

How do I remember the irregular shape of fosse since it doesn't look like ser?

For irregular verbs, a great trick is to look at the 'they' form in the simple past (Pretérito Perfeito). For ser, 'they were' is foram. Drop the -ram ending and add the Imperfect Subjunctive endings (-sse, -sses, -sse, -ssemos, -ssem). That leaves you with fosse for the dragon.

Why does the second half of the sentence use voava (used to fly) instead of the conditional voaria (would fly)?

In European Portuguese, people usually swap out the Conditional tense for the Imperfect Indicative (voava) in everyday conversation. So even though it literally looks like 'used to fly', in an 'if' sentence like this, it translates to 'would fly'. You can still use voaria, but voava sounds much more natural when speaking.

I thought 'smaller' was menor. Why does this sentence use ?