Effects that modify a creature's power and/or toughness will apply to the creature no matter when they started to take effect
Its effect does not activate when you summon it therefore its effect to summon can not be negated, only the summon can
Glissa, Herald of Predation generates a good board presence over multiple turns
Instead of stacking +1/+1 counters, perhaps the new version would allow you to distribute -1/-1 counters, making this card deadly to creatures as well as other permanents on the board
Hiu ng gc (EN): When a Spell/Trap Card, or monster effect, is activated that includes an effect that Special Summons a monster(s): Return to the Extra Deck, 1 face-up Fusion Monster you control, or 2 Fusion Monsters in your GY, that mention "Fallen of Albaz" as material, and if you do, negate the activation, and if you do that, destroy that card