It feels overpriced for what it is - the poison ability is useful no doubt, but can be countered/removed. In a no abilities match, sure, that would work well (assuming not against a Llama with the cleanse to resolve it). The bulk of other legendary summoners provide a base stat buff/debuff, rather than all abilities too. A 3 mana legendary opens up some options for death, in little league battles, though I think I'd rather take a 4 mana Quix to gain access to Dragon cards (if applicable). That all depends on ruleset/deck build though.
In contrast, while the other legendary summoners are more costly for the most part, there's a wider range of applicable scenarios IMO and the abilities don't have a 50% activation rate. Some food for thought, like !PIZZA