Now that there's a 50% increase in transcendence rates, here's a way to further reduce the number of fodder heroes used to EX your heroes (this works outside of the transcendence event as well)
Are you familiar with this situation below ?
Heroes in Legion Of Heroes have 4 ranks of progression: A (Blue) < S (Yellow) < SS (Red) < EX (Purple). There's only 1 rule to note when ranking up heroes efficiently: Transcending 2 identical heroes of the same rank have a 100% chance to rank up, i.e. if I used a rank A Lacita to rank up the above, it'd be 100% chance of success, so instead of using 13 heroes, I only use 2, saving 11,000 legendary essences (That's a whooping 110 rank 6 tickets from tower)
If you apply the same concept to rank up to EX, you only need to use 8 duplicates of the same hero to EX. For the higher season and thus rarer heroes, I'll use my duplicate heroes not in knight system to bring up the rare heroes to rank SS first. After that, I'll transcend 2 rank SS together for 100% chance to EX, as shown below:
Rank A Lacita + Rank A Lacita = Rank S Lacita (100% chance)
Rank S Lacita + Rank S Lacita = Rank SS Lacita (100% chance)
Rank SS Lacita + Rank SS Lacita = Rank EX Lacita (100% chance)