Problem-first upgrade guide
Upgrade the bottleneck
The public description names Power, Health, Speed, trails and auras. It does not publish a universal best order, so start from the problem you can observe.
Symptom → check → action
Low damageCheck Power, equipped card level and active boosts.
Low survivalCheck Health and whether movement avoids damage.
Slow routeCheck Speed before assuming a stronger card is required.
Mixed problemChange one upgrade category, then compare the next run.