Common mistakes
The root ends in و or ي, and the endings themselves change. Three patterns cover it: دَعَا يَدْعُو, رَمَى يَرْمِي and نَسِيَ يَنْسَى.
اِنْتَهَيَ → اِنْتَهَى Past: heاِنْتَهَيَتْ → اِنْتَهَتْ Past: sheاِنْتَهَيُوا → اِنْتَهَوْا Past: they (m.)يَنْتَهِيُ → يَنْتَهِي Present: he