About balancing on first creature, I choose Turtle, for Tank + Grinding, though Lv15 can Dig-In + SV + D can kick Maiasaura easily. Allosino for backup, and it can also use as real hitter.
Tips: Self-Cleansing + Deceleration Plus an Instant Hitter
Recommend: Resistance (Deceleration), High Hp / Heavy Attack Deceleration (1T) Distraction, Evasion (mainly on IR from Maiasaura) ... https://www.youtube.com/watch?v=WgC1jMcYVQ8
Blue for Full Immunity on Countering Monolophosaurus and Scorpios Rex Gen 2, if you don't know why, you know now.
Tips:
** Try to leave Distraction User on S.rex G2 for better process
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https://www.youtube.com/watch?v=EUPKys5iD9o
It's not that hard with Turtle, everyone can dart and collect Turtle DNA from the map, so, a free incubator.
And an extra slot still there, you can try new method whatever you want.
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https://www.youtube.com/watch?v=SVBSii88uvk