What does crafting a legendary Anipod unlock?

The pod is the key, not the prize. You build it from legendary tokens, which come out of ordinary play: open-world exploration, catching, and main story progression. The moment the pod exists, the encounter opens on the map.

What happens there is not a catch rate. Beat Irisalis in the scripted fight, throw the crafted pod, and the bond is sealed. Guaranteed, not random. The flip side is that the narrative boss encounter can only be completed once. It closes behind you, so there is no farming it for a second copy.

What the Irisalis fight throws at you

Irisalis is a Grass-element DPS and a legendary encounter boss. Her trait, Bloom Cluster, revives her when she is Fainted: she turns into a flower, blooms again and restores her own vitality. It can trigger once every 180 seconds, so plan on putting her down more than once.

She also generates clones that add to her damage output. Whenever she lands the final hit of a basic attack combo or casts Whirling Blossom Rain, the clones fire a Floral Gleam Beam at the target. Her ultimate, Florae Descent, leaves another clone behind on the field. Bloom Cluster additionally lowers the EP cost of her next ability once a clone has landed 9 hits on a target, so the longer the clones stay up, the cheaper her rotation gets.

The other route to the legendary Aniimo

Crafting was not the only way in. The third beta ran an Irisalis event that handed out the legendary through gacha with limited resources and pity guarantees. Entry ran on Glimmer, with legendary pity landing somewhere between 4,500 and 6,000. The Stamps Shop is also worth watching in your first week, since its weekly refresh includes a chance at Irisalis among its items.

Not settled: How players acquire Irisalis is still being reworked at Kingsglory in response to player feedback, so the token-and-craft route is not locked in for launch.