Invasion of Segovia is a perfect example: It creates Kraken tokens, so its already synergistic, and it makes fodder for Jalira, but its not a creature card, so this otherwise subpar hit wont ever be the card you find with Jaliras polymorph ability
If the target nonland permanent is an illegal target as Compelling Deterrence tries to resolve, it won't resolve and none of its effects will happen
Finally, when Slinza or any other creature with a power of four or more comes into play under your control, you can pay two mana to have Slinza fight another creature
There was also a big concern that, if a Universes Beyond card was powerful enough to see play in eternal formats, the price could escalate forever (as it could never be reprinted without a licensing deal)
Rather than being slow and clunky it is brutally efficient, which is why it is banned in modern