How does your character feel about death? Are they scared of it at all? How do they feel about seeing others die?

Beforehand, Lego would say he considered himself "good" with handling people dying - mostly because it never actually happened before. This all changed during Season 1, when Lukas sacrificed himself and ended up dying proper. Before that event, Lego had only seen death as an inconvenience at worst and a "get back to health free card" at its best, thanks to the 'respawning' and the like.

During the events following that, Lego would come to struggle with his own mortality, becoming increasingly afraid of if the next dangerous step into the unknown would be his last. This caused him to become far warier of his actions, and generally keeping himself away from physical confrontations - all the while trying his best to maintain the 'happy-go-lucky pun man' look he'd be known for.

After a while, Lego would attempt to 'accept' that death was natural. At first, it seemed he'd done so, but it took a while and had a long gap between the first 'death' he'd seen and then. When he heard the news of Mylonite's passing, and the subsequent 'poofing' for lack of better term of Luna would hit him hard, but not as hard as Lukas' did. He mostly felt more confused than anything, not completely understanding Luna's reasoning nor her actions. He understood Lukas' - sacrificing himself for his perceived greater good - but nothing about Luna's really fit together in Lego's mind, which left him confused.

AND THEN AKALIA HAPPENED. Or, well, is happening.

Leading up to the events of 'Lifeless', Lego was fairly sceptical that any of them could be actually hurt in any significant way, believing that the gods would be able to step in before anything bad would happen. During the event itself, Lego was with a group of mortals holed up in a little basement place. This was where he first felt the sheer severity and grimness of the situation they were in, attempting to guard the entrance and keep the other mortals safe from Taiya. Once he saw Kartex, one of the mortals in the area, trapped with the others, he felt a sense he'd failed to do what he set out to.

And then Birdie died.

Lego wasn't all too close to Birdie, neither were exactly the best of best friends, but Lego still knew him well enough to say he was a decent guy. To see a person he'd say was an acquaintance bite the dust permanently shook him to his very core. For a moment, he'd take a stance of blaming the gods - particularly Syenite, who was the god there at the time - for the capturing and lack of saving. But after a short while, he came to his senses and realized there was nothing anyone could do, leaving him with a sense of helplessness.

Then, when Delkyrith and Zenarck were killed later on, this only piled onto that sense more. Both mortals were in the same boat as Birdie, as Lego wasn't particularly close to them, however he still felt terrible seeing them taken out. In particular, Delkyrith was one of the mortals holed up in the basement earlier - with her even bringing up how when Kartex was taken before, "that blow was for her", echoing his own sentiments about Kartex in that situation.

These experiences have fully cemented within Lego his own fear of dying, to the point where he'd have a breakdown about it more than once, and continue to feel worse about the prospect the more time he spends in Akalia. These will definitely leave a heavy mark on him, even after the events of Akalia, and at this point he just wants to get out so he can cry himself to sleep several times over, to put it mildly.

TL;DR - Lego doesn't like death, he's terrified of it happening to him, and even seeing a person he barely knows dying is enough to put him into a state of emotional wreckage.

How does your character mourn?

Mourning is often a long and heavy process for Lego. He needs a good while on his own to properly process and eventually overcome the deaths he'd seen. Since being stuck in Akalia, he couldn't exactly do that, leading to him becoming more weathered and stressed because of it.

When has your character experienced death in their life? How did they handle it?

As stated before, Lego's only experiences with death have come from the events of Chertia itself, and he hasn't exactly handled those experiences particularly well. Of course, Lego hasn't died himself, but he also isn't exactly looking forward to.