Axie part evolutions generally come with 10 heal/shield/attack per energy cost, so 2 cost attacks go up by 20 (sandal only 15 but the effect is way too strong even so). Multi hit attacks go up by 3-5 (if has an effect). Aoe heals and shields usually also just 5 by for 3 axies has a potential of 15 value. These cards are all the rest that has a custom effect/upgrade. This includes: -all the draw cards -all the cards that help pulling other cards -all powers -most of poison cards -most of spike related cards -most of utility cards, especially 0 cost -some attacks with effects or utility These cards generally worth upgrading as they define your strategy. Keep in mind the cost, if you have a plant with innocent lamb, upgrade lamb first, then any plant card, since it's cheaper to buy mementos. First two levels matter most as you can reach 10 within 1-2 days (with other games giving axp) and 20 after a season. To reach 30, that axie has to be used in a lot of games on a good winrate. One other card that is pretty good upgraded is hermit, since the effect activates for 40 shield, which on normal hermit is 40/70 but hermit+ can activate twice on 40/80 without other shield cards.