Ok, so there’s two different effects heroes can give for mana that sound alike, but are quite different. They are mana generation and mana regeneration.
Mana generation happens on offense when you match tiles or pop dragon heads and send the tiles up into the enemy. Mana generation happens on defense when raid or war defenders get hit with tiles. Think of this as working at on hourly job: work X hours, get $Y (i.e. hit with X tiles, get Y mana).
Mana regeneration is something that just gets added to your hero each turn. This of this as an allowance: each week, you get $X (i.e. each turn, you get Y mana). Alberich is one hero that gives mana regeneration. Defending raid and war heroes also regenerate the equivalent of 1 tile of mana per turn.
Heroes that affect mana generation and regeneration:
Lancelot, Khagan, & Friar Tuck: they add +X% to your mana generation. This means when you match tiles. It doesn’t affect regeneration such as Alberich.
Hel, Natalya, & Little John: These cards affect mana generation (i.e. mana from tile matches), but NOT regeneration. This means cards under the effect of Hel/LJ/Nat and Alberich will still regenerate Albi’s mana each turn as usual.
If there are other heroes with mana gen/regen that I missed, please let me know and hopefully the explanation was clear enough.
EDIT: added Nat and Friar Tuck