Erlidominus is tricky, cause of its low health. I usually start with Rampage. When I face Thor I usually use cloak as I know Erlidominus won’t survive two hits without it and will oneshot Thor if dodges at least one attack.
When facing Utarinex I would also recomend cloak first turn. I killed several Erlidominus with Utarinex when they went Rampage then cloak. Instant charge hitted through cloak.
When you don’t oneshot oponent, then finish it of with Minimal speedup strike as that way will be faster as any other dino.
Its not a good opener as any dino that has enough health that survives Rampage, can kill it. Erli Rampage damage is same as its health (damage is rounded upwards: if health is 2721, damage is 2722).
Tryko is it’s worst matchup. Cloak only to avoid counter attack damage or when you are sure that Tryko already used Instant invincibility. Also Strike and run only if Erli has enough damage to survive counter.
Second worst matchup for Erli is Monostego as it can nullify cloak.
EDIT: Each additional level means higher survivability for Erli.