What about giving it low base stats, but an attack with a high multiplier, greater than 2 (so more than a rampage), as opposed to giving it a new passive ability ? It would be like the opposite of Koolabourgiana, in that sense.
How about a new attack, like “Swarm: priority. Cleanse. Regenerate 100% health. Gain priority for 2 turns. Attack damage x3 for two turns. 3-turn cooldown.” That used in conjunction with rending strike or maybe a different rending move would do some serious damage.
It could have Immunity as a passive ability, and a distracting move or two, maybe even “Debilitating Distraction”.
Other ideas: A wounding (bleed) move would make sense for Troodon, and maybe, instead of a stat-multiplying move like “Swarm”, it could have a status-effect multiplier. For example, if the multiplier was 3, any bleed damage done to the opponent would be multiplied by 3, any distracting move would nerf the opponent’s attack damage by three times as much, etc.
Swap-in ability, if any, could be swap in evasion/dodge.