[mal-2]

Bluesky has a 300 character limit, Mastodon has 500, non-Mastodon ActivityPub servers have a configurable limit. Mastodon can render markdown, has subject lines which are commonly used as content warning tags, can translate posts. It supports custom emoji and non-Mastodon ActivityPub servers support custom emoji reactions. Bluesky has more discovery features like community-curated lists and algorithmic suggestions of who to follow.

[anotherevan]

The character limit depends on which Mastodon instance you're on. 500 does seem to be the norm. The one I use is 3000.

[mal-2]

Partially true, but vanilla Mastodon does hardcode it at 500. Some forks make it configurable (I believe glitch-soc does), and some admins have edited the hardcoded value manually.