Contined from Rules Questions, as it’s an off-topic discussion for that thread.
There are more cards that specifically combo with Time Spiral than with Hallucination, but there are several cards that specifically combo with Hallucination: Dreamscape; Hallucination; Macciatus, the Whisperer; Reteller of Truths; and Liberty Gryphon, and furthermore any card that’s capable of targeting can synergize with Dreamscape or Hallucination to destroy units. I would argue that Skeletal Archery is more narrow in focus and less flexible in usage.
What makes Hallucination tricky is that it has to be played in the same turn as the other card in question, except for the rare case of a Truth mirror match. But considering its extraordinary potential return on investment ($2 and a card is worth more than 2 units at $1 and a card each, and it can even affect expensive tech II units), IMO it’s worth it. Furthermore, where mono-Blue is concerned, at least Bigby brings stash to the table. Also, out of all the colors, Blue’s design seems to be the most combo-oriented.
IMO the reason Hallucination doesn’t see more play has less to do with its limitations than with the fact that in many cases it’s overshadowed by similar effects from other cards, especially Dreamscape, $1 spells that let you draw (Boot Camp/Appel Stomp), and cards that target at no cost (Blooming Ancient/Drill Sereant especially as they don’t need to exhaust). Hallucination’s main advantage over Dreamscape is that you can use without exposing your own units to target death, which is helpful when you don’t have access to Macciatus, but want to be able to target-kill enemy units. Best-case scenario for Hallucination is probably if you’re running Truth with Finesse, Peace, or Growth, don’t want to spec into Truth, are facing an opponent who can target multiple things per turn, and have access to no Flagbearer other than Spectral Flagbearer. That’s a fairly niche scenario. Well, also you’d want to use it if both of your Dreamscape copies were trashed by Nature Reclaims.