C Common Umbral Horror Will o' the Wisp X DARK Level 1 [ FiendEffect ] ATK 0 DEF 0 When this card is Normal or Special Summoned: You can target 1 "Umbral Horror" monster you control or in your Graveyard, except this card
My first thought is to mitigate the cost of spells that have strive, like Call the Coppercoats or Phalanx Formation
For example, the effect on Rivaz of the Claw allows you to cast Fallaji Dragon Engine from your graveyard for either its normal cost or its prototype cost
Monsters stolen by Paradox are changed into evil Malefic forms
All is Dust is a bit more immediate and tends to deal with planeswalkers as well but is prohibitively costly for most decks to be considering and ends up being quite a niche card used in quirky decks like mono green ramp control and completely colourless lists
While some games still ended around Turn 7-8, the journey to get there was often ended abruptly by a combo, rather than someone curving out