Relentless Assault variants tend to be win-more and they dont typically make their way into Cubes, but there are some Sacrifice synergies going on here with the morbid cost reduction and the +2/+2 and haste to give this card some wider applications
If they guessed right, sacrifice The Toymaker's Trap
Displacer Kitten Displacer Kitten is an odd-ball because it was printed during the era of this ability triggers only once per turn effects, and yet that text isnt present on such an obviously broken ability
It's also good in spell-slinging decks, or Storm decks like well, Storm
The idea is to combine it with Solemnity and each time you receive damage, Nine Lives wont get any counters and you wont receive any damage
ESPER SENTINEL A moment ago I mentioned card advantage and white, and so you might be able to connect the dots as to why Esper Sentinel is at spot #2 on this list