Vishgraz, the Doomhive

The bonus Vishgraz receives due to its last ability may cause it to survive combat damage in some cases. For example, if an attacking Vishgraz is blocked by a 3/3 and another creature with toxic 1 is attacking at the same time and is unblocked, Vishgraz with deal 3 damage, receive 3 damage, and get +1/+1 at exactly the same time. The end result is that it will stay alive and be a 4/4 creature with 3 damage marked on it.

Damage dealt by a creature with toxic grants the same number of counters regardless of how much damage is dealt. Notably, if a replacement effect modifies the damage in some way (such as that of Gratuitous Violence), the number of counters given remains unchanged.

A player with ten or more poison counters loses the game. This is a state-based action and doesn't use the stack. In other words, it happens immediately and players can't respond to it, just like a player losing the game due to having 0 or less life.

Multiple instances of toxic are cumulative. For example, if a creature has toxic 2 and gains toxic 1 due to another effect, combat damage that creature deals to a player will cause that player to get 3 poison counters.