I activate Lanista effect at the end of battle phase after i attack, to tag back to laquari. after i sp. summon laquari, he activate warning to negate the summon of laquari. is this legal, or does he have to warning the effect of lanista instead?
He has to warning the Lanista, since it was through Lanista's effect that Laquari was summoned.
When Lanista uses its effect, its cost sends it back to the deck. Warning can be chained from then, causing Lanista to "die" in the deck, negating its effect.