Since leaning on mutate is a relatively risky strategy, it's nice to have a way to get these cards back from the graveyard
So they ended up with flashback, but you can tap a creature to cast it for cheaper. WotC considers flashback as deciduous, or a mechanic that they plan to reuse fairly often (although not in every MTG set)
The other common way to boost damage is Crobat G (G)
BOING, Fox Mim on the board to send Merlin back to hand for another point of lore, and to Rush any opposing cards
Magic creator Richard Garfield may have had innocent intentions when he decided to distribute his new card game primarily through randomized booster packs, and to make stronger and more exciting cards less likely to appear in said boosters than the common chaff
That may seem simple, but it did facilitate some combos back in the day